Microfluidic Synthesis of Semiconducting Colloidal Quantum Dots and

Subscriber access provided by EDINBURGH UNIVERSITY LIBRARY | @ http://www.lib.ed.ac.uk

Review

Microfluidic Synthesis of Semiconducting Colloidal Quantum Dots and their Applications Subbiramaniyan Kubendhiran, Zhen Bao, Kashyap Dave, and Ru-Shi Liu ACS Appl. Nano Mater., Just Accepted Manuscript • Publication Date (Web): 26 Mar 2019 Downloaded from http://pubs.acs.org on March 26, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Nano Materials

Microfluidic Synthesis of Semiconducting Colloidal Quantum Dots and their Applications Subbiramaniyan Kubendhiran,†,‡ Zhen Bao,† Kashyap Dave,†,# and Ru-Shi Liu*,†,§,║

†Department ‡Genomics

of Chemistry, National Taiwan University, Taipei 106, Taiwan

Research Center, Academia Sinica, Taipei, Taiwan

Nanoscience and Technology Program, Taiwan International Graduate Program,

#

Academia Sinica and National Taiwan University, Taipei 115, Taiwan §Advanced

Research Center of Green Materials Science and Technology, National Taiwan

University, Taipei 106, Taiwan ║Department

of Mechanical Engineering and Graduate Institute of Manufacturing

Technology, National Taipei University of Technology, Taipei 106, Taiwan E-mail: [email protected] (RSL); Fax: +886-2-33668671; Tel: +886-2-33661169

1 ACS Paragon Plus Environment

ACS Applied Nano Materials 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract The large-scale synthesis of high-quality quantum dots (QDs) for commercial applications, such as lighting, displays, and biomedical devices, is an urgent necessity. Batch reactor systems present a number of problems, such as improper mixing, heating, and reagent addition. Hence, controlling the growth and size of nanocrystals is difficult in this type of system. A number of microfluidic techniques have been developed to enable semiconductor colloidal QD synthesis. The reaction parameters of these techniques are controlled precisely during synthesis. Over the last 16 years, many advancements have been introduced to achieve products similar to those obtained from batch systems. Multiphase flow reactors reduce reactor fouling by using immiscible carrier liquids, which decrease contact between reagents and the channel wall. Online monitoring of nanocrystal growth through absorbance and fluorescence spectrometry provides detailed information on the reaction parameters. Chip-based reactors with sub-channels decrease backflow and control the addition of reagents. In this review, we discuss all aspects and developments in microfluidic systems for the production and applications of QDs.

KEYWORDS: quantum dots, microfluidic technique, large scale synthesis, droplet based chip reactor, in-line optical detection, high-quality.


Page 2 of 72

Page 3 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. INDRODUCTION Quantum dots (QDs) are semiconducting nanocrystals or nanoparticles with diameters in the nanometer range. Over the last 20 years, QDs have emerged as innovative materials and gained importance in nanotechnology and nanoscale science.1-5 Based on their elemental composition, QDs can be classified into four major types, namely, group II–VI (e.g., CdSe, 6-9 CdS,10 CdTe, 11-12 ZnSe

13),

group III–V (e.g., InP

14

and InAs

15),

group I–III–VI (e.g., CuInS2 16), and perovskites (e.g., CsPbX3, X = Cl, Br, I).17-18 The many advantages of QDs, which include narrow emission, tunable wavelength, high photoluminescence (PL), spectral purity, and photo-chemical stability, make them promising materials to replace conventional organic dyes.1, 3, 19-21 In particular, the sizedependent emission of QDs allows tuning of the emission wavelength from ultraviolet (UV) to infrared.22-23 Besides, core–shell-structured QDs exhibit enhanced emission by passivating defect-sensitive cores and suppressing non-radiative recombination.24 Shell layers are grown on the surface of the core. The materials used for the shell could be of the same or different groups of inorganic materials. The following key physical parameters are followed when selecting a suitable shell material: (a) the material should contain a band gap higher than that of the core,25 (b) the lattice constant of the selected shell material should be close to that of the core to alleviate lattice strain and accelerate shell growth,26 and (c) the conduction and valence band positions of the shell materials should be higher than those of the core.27 Based on band alignment, core-shell systems can be further classified as type I or type II.28 In type I shell materials, the valence band edge position is lower and the conduction band edge is higher compared with those of the core. Thus, charge carriers are confined to the core. Core-shell structured InP/ZnS,29-32 InP/ZnSe,33



InP/ZnSeS,34 and InP/ZnCdSe2 35 are the best examples of the type I system. Conversely, in type II core-shell system, both conduction and valence band edges are positioned above or below the core.36 Consequently, one charge carrier is confined to the shell, leading to redshifting of the emission wavelength (i.e., InP/CdS).37 Colloidal organic/inorganic metal-halide perovskite nanocrystals have been developed as inexpensive semiconductor materials for commercial light-emitting diodes (LEDs), backlight display, photovoltaic and biological applications.38-43 The present review focuses on the microfluidic synthesis of the four major types of QDs, i.e., (i) QDs based on group II–VI elements, (ii) QDs based on group III–V elements, (iii) QDs based on group I–III–VI elements, and (iv) perovskite QDs. 2. APPLICATIONS OF QDs QDs has been used in various technologically and economically important fields such as solid-state lighting, display, photovoltaics, lasing, biomedical, biological labeling and detection, etc. The major advantages of colloidal QDs such as solution processability and spectral tuning are attracted great attention in optoelectronics application.44 Significantly, the QDs provides huge benefits to the design of optoelectronic devices. For instance, the size dependent spectral tuning furnishing color mixing in LEDs and reduce the production cost by eliminating the optical filters which cause loss of signal in photodetection.45 Moreover, solution processing facilitates the low cost large-scale production of optoelectronic devices. Recently, white LEDs (WLEDs) are considered as a superior choice and promising alternative to fluorescent tubes and standard incandescent light bulbs in most lighting applications. The WLEDs are exhibiting longer operating lifetimes and significant energy savings rather than conventional incandescent light bulbs.46 Nowadays, a range of QD-WLEDs exhibit excellent potential in meeting this need.


Page 4 of 72

Page 5 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Furthermore, solar energy conversion to electricity is one of the most developed areas of QDs application. Whereas, the semiconducting colloidal QDs are ideally fulfilling the requirements of third-generation photovoltaics with low cost and high efficiency. QDs exhibit wider absorption profile and superior photostability than conventional organic dyes or metal complexes.47 In QD-sensitized solar cells, an expensive and less stable ruthenium(II) bipyridine dye was replaced by QDs and act as sensitizers to the TiO2 semiconductor layer. Importantly, QDs are being exploited for a different kind of biologically oriented applications which include in vivo bioimaging, drug delivery and in vitro biosensor applications. 2, 48 In biomedical applications, the QD surface is modified with different kinds of molecules which makes them biocompatible.49 So far, the QDs are integrated various nanomaterials including carbon allotropes, upconversion nanoparticles, noble metal nanomaterials, metal-organic frameworks and metal oxides.50 Furthermore, the QDs exhibit high quantum yield and high stability in aqueous solutions which is suitable for fluorescence sensing. In this review, three important applications of QDs: (i) semiconducting colloidal QDs for QD-LED and QLED applications, (ii) photodetector and lasing applications (iii) bio-applications, including bio-sensing and bio-imaging addressed briefly. 2.1. Semiconducting colloidal QDs for display, QD-LED and QLED applications. Future electronic devices and their components based on wireless systems are used to connect displays by acting as information output and input ports (Figure 1a). Among the various types of LEDs available, such as organic LEDs (OLEDs), 41, 53 polymer LEDs

54,

and QLEDs,55 the latter show unique advantages, including size-dependent

emission (Figure 1b), high color purity, wide color gamut, excellent stability, low turn-on



voltage, ultrathin form factor, and high brightness.56 QDs can be excited both electrically and optically lead to electroluminescence (EL) and photoluminescence (PL). The principle of electrically excited QDs is based on the direct injection of charge carriers into the QDs. The corresponding light emitted is due to radiative recombination of the injected charge carriers in QDs with various sizes and emission colors. For optically excited QDs, a different color emitting QD combination is used to generate light; here, the QDs are used as nanophosphors. QLEDs exhibit brightness of up to ~200,000 cd m−2, distinct color purity (full width at half maximum [FWHM], ~30 nm), operability at low voltages (V turn-on < 2 V), and simpler processing than other types of LEDs.1,55,57 Moreover, recent developments in patterning techniques have helped improve the resolution of full-color QLED arrays, which was not previously possible with traditional display-processing techniques (e.g., the shadow masking technique for OLEDs). 58-59 Researchers should pay careful attention to the following parameters to improve the performance of QLEDs for full-color displays: (i) material design, (ii) device structure and principles of operation, and (iii) pattering technology of QDs. For instance, CdSe QDs exhibit a higher color purity (FWHM of ~30 nm) and wider color gamut than commercial high-definition television (Figure 1c).56, 60-62 Core–shell-structured colloidal QDs show improved PL quantum yield (PLQY) and stability, which enhances their external quantum efficiency (EQE). 63 The shell thickness plays a beneficial role in the EL efficiency of QDs. During light emission, a thicker shell can alleviate the charging of QDs, which is attributed to their improved EL efficiency (Figure 1d).64 The elemental constitution of the intermediate shells affects the EL properties of QDs (Figure 1e-f). 65 In comparison with CdS-rich intermediate shells, ZnSe-rich intermediate shells display excellent EL properties


Page 6 of 72

Page 7 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


because of their low barrier during carrier injection (Figures 1g–h).66 Oh et al.67 synthesized CdS/CdSe/ZnSe double-heterojunction nanorods for QLED applications (Figure 1i) and achieved superior EL performance with a maximum brightness of 76,000 cd m−2 and remarkable peak EQE of 12%. However, Cd-based QDs are toxic to the environment and harmful to the human body.68-72 Wearable displays, for example, are in direct contact with the human body. Hence, the development of Cd-free QLEDs is required to produce next-generation displays. Cadmium (Cd)-based QDs are gradually being replaced by III–V InP QDs, which are considered excellent alternatives due to their narrow emission and tunable emission wavelength covering the whole range of the visible spectrum.71 Core–shell-structured green InP QDs exhibit good EL performance with record brightness reaching ~10,490 cd m−2 and an EQE of 3.4% (Figure 1j).73 Group I–III–VItype semiconductor QDs are another alternative to Cd-based QDs. 74-76 However, the broad emission spectra (FWHM: ~100 nm) of these QDs is a major drawback affecting their color purity (Figures 1k–l). 77-79 Figure 2 shows the applications of the semiconducting colloidal QDs. 2.2. Photodetector and Lasing applications. A photodetector device was used for measuring and/or detecting the properties of light through the photoelectric effect, which generally represent as a photocurrent.80 Nowadays, the nanostructured photodetectors received enormous interest in both industrial and academic fields owing to their superior performance in various applications including optical communication, image sensing, environmental monitoring, and biological/ chemical detection.81-83. Especially, colloidal QD photodetectors exhibited an excellent performance with good spectral selectivity.84 In addition, the size dependent optical property of the QDs can be used to obtain the spectral



Page 8 of 72

bands with different wavelengths. For instance, the spectral band was varied from the visible to the mid-infrared and short-wave infrared.85-87 Over the past few years, different kinds of QD materials such as perovskite,88 ZnO,89 and PbS

90

have been extensively

studied and implying their great potentials for the photodetector application. Recently, Kan et al

91

reported the article based on the ZnS QDs for the design and fabrication deep

ultraviolet (DUV) photodetectors. The DUV detectors are can be used in satellites, missileplume detection, and secure communications.92-93 The reported ZnS QD based device displayed high response speed (rise time: 28 μs and decay time: 0.75 ms) and excellent selectivity for the DUV light. On the other hand, the perovskite QDs have been extensively studied in photodetector applications.94 The illustrious advantages of the perovskite– organic hybrid photodetectors such as high charge carrier mobility, tunable optical bandgap and facile solution-processing properties attracted more attention than other kinds of semiconducting materials.95-98, Owing to their remarkable properties, the perovskite– organic hybrid photodetectors exhibit superior performances, special wavelength detection and extend the spectral detection region.99-100 Further, perovskite–organic hybrid photodetectors are alternative for the single functional model and meet the requirements of versatility in commercial applications.94 Recently, most of the researchers are applied the perovskite QDs for lasing application because of its low threshold and temperature insensitive optical gain properties.101 For instance, Zhu et al.102 used organic-inorganic lead halide perovskite CH3NH3PbI3 nanowire at 402 nm laser excitation for the lasing application. In their work, the authors approached very low lasing threshold 220 nJ/cm2 and high quality factor of 3600]. Huang et al.103 reported an ultralow lasing threshold (0.39 μJ/cm2) from a hybrid vertical cavity surface emitting laser structure which containing two


Page 9 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


highly reflective distributed Bragg reflectors and CsPbBr3 QD thin film. Later, Chen et al.104 synthesized the lead free CsSnI3 perovskite QDs in cholesteric liquid crystal and reported the ultra-low threshold 150 nJ/pulse and narrow line width of 0.20 nm. 2.3. Biomedical applications of QDs. Semiconducting colloidal QDs have been utilized in various biomedical applications, specifically in gene technology, drug delivery, fluorescent labeling of cellular proteins, in-vivo animal imaging, cell tracking, tumor biology investigation, and pathogen and toxin detection.105 The eminent properties of QDs, such as their size tunability, high brightness, long lifetime, and narrow luminescence,106 make them promising alternatives to organic fluorescence dyes. In comparison, the QDs improve the stability against photobleaching which is 100 times higher than organic dyes and the brightness is 20 times higher than organic dyes.107 As a consequence, the QDs enhances the sensitivity and repeatability in complex sample analysis. Another major advantage of QD is the facile surface modification with various sensing elements such as peptides, DNAs and antibodies for the construction of QD-labelled probes.107 On the other hand, near-infrared (NIR) light with emission wavelengths longer than 650 nm greatly can enhance the potential of fluorescence in biological applications because of its low autofluorescence and absorption.108 Auto-fluorescence is a major problem limiting in vivo imaging. For example, “green” auto-fluorescence is observed when an anatomical mouse is excited with blue light. Auto-fluorescence is also high in the small intestine, bladder, and gallbladder.109-110 Likewise, biologically essential molecules, including fatty acids, porphyrins, collagen, NADPH, and flavins, exhibit strong auto-fluorescence from both ends of the visible spectrum.111-112 Thus, the current researches focused the attention on the two NIR biological windows.113 The wavelength ranges of 650–950 nm (NIR1) and 1000– 9 ACS Paragon Plus Environment


1350 nm (NIR2) attracted more attention for in-vivo applications (Figure 3a).114 Owing to the low absorption of water, oxygenated hemoglobin, and hemoglobin in these spectral regions, light can penetrate strongly into biological tissues (Figure 3b).115 As well as, lower endogenous fluorescence observed in these spectral regions.116 Cd-based NIR QDs, such as CdTe/ZnS, CdTe/CdS, and CdTe/CdSe, were first used in biological applications.117 However, Cd-based QDs are restricted due to their cytotoxicity in vitro under extreme conditions.118 Hence, the development of Cd-, lead (Pb)- and mercury (Hg)-free NIR QDs has attracted great attention in recent years. For instance, core–shell-structured CuInS2/ZnS QDs with 80% PLQY were synthesized, and their emission was found to be tunable from the visible to the NIR spectral regions.119 CuInS/ZnS QDs, as all-in-one theranostic nanomedicines coupled with intrinsic fluorescence/photoacoustic imaging, can be applied to tumor phototherapy (Figure 3c).120 In- and As-based III–V group QDs play a major role in bioimaging applications. Aharoni et al.121 synthesized InAs/CdSe/ZnSe core-shell structures with 70% PLQY and emission that could be tuned from 885 nm to 1425 nm by varying their shell thickness. Gao et al.122 synthesized InAs/ InP/ZnSe NIR QDs with the NIR emission of 800 nm for the tumortargeted imaging application. Moreover, the QDs were successfully utilized in electrochemical sensor applications. Li et al.123 reported the streptavidin-coated CdSe/ZnS QDs for the stripping voltammetric detection of telomerase at the single-cell level. The authors observed that the QDs based assay technique is very simple and doesn’t require complicated labelling and hairpin probe design.


Page 10 of 72

Page 11 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3. MICROFLUIDIC SYNTHESIS TECHNIQUE Owing to the wide applications of QDs and increasing demands for these materials, QD synthesis techniques have evolved extensively over the last 20 years. Two important synthetic approaches, namely, vapor-phase epitaxial growth and liquid-phase methods, have emerged to produce different types of QDs.

23,124

Vapor-phase epitaxial growth

methods have been utilized successfully to synthesize size-tunable QDs. Significant disadvantages, such as difficulty in separating the product from the substrate and the use of sophisticated instruments, however, hamper the continuous use of this technique.125-126 The liquid-phase technique involves a series of chemical reactions that can produce highly dispersed colloidal QDs with low energy requirements. The liquid-phase synthesis method can be further categorized into biosynthesis,127-128 non-injection organometallic synthesis, 129-130

hot-injection organometallic synthesis,

131-132

and aqueous synthesis.133-134 These

methods can provide the following advantages over the epitaxial growth technique: (i) control of the shape, size, and framework of the QDs; (ii) modification of the functionality and solubility of the QDs by ligand-exchange; and (iii) the solvent processability accelerate the economic deposition techniques and device fabrication.24 Nevertheless, the drawbacks of liquid-phase synthesis methods, such as their slow precursor mixing, heating, cooling, low productivity, and poor reproducibility, limit the large-scale synthesis of QDs.135 Reproducibility is the main drawback in conventional batch synthesis processes due to difficulties associated with inconsistent reaction conditions. Environmental conditions, rates of precursor addition, and manual errors affect the quality of the final product. Hence, alternative quality-assured batch synthesis techniques must be developed to prepare QDs with superior shape and size selectivity, batch-to-batch reproducibility, and stringent



control over particle properties.136 The synthesis of colloidal QDs is quite difficult because chemical reactions are highly responsive to experimental conditions, such as reaction temperature, kinetics, and caustic precursors. Today, the microfluidic synthesis of colloidal QDs is a more promising technique than conventional batch synthesis techniques. The benefits of microfluidic synthesis are as follows: (i) efficient mixing, (ii) high heat and mass transfer, (iii) high surface-to-volume ratio, (iii) temperature control, (iv) continuous production, and (v) low reagent consumption emphasis; as such, microfluidic synthesis is an ideal technique for large-scale production.137 Edel et al.138 first reported the preparation of colloidal QDs based on a microfluidic system in the year of 2002. Inspired by this work, many studies have reported the synthesis of various types of QDs. Microfluidic reactors can be classified into two main categories: capillary-based reactors and chip-based reactors.139-141 Capillary reactors are noncomplex in structure. In addition, uncomplicated fabrication process using simple fluidic parts, which are joined by suitable lengths of tubing.142 Chip-based reactor systems can be fabricated using glass, plastic, or silicon substrate through three main techniques: wet etching, soft-lithography, and micromachining.143 For instance, multiple chemical processes involving reagent addition, mixing, heating, and cooling components can be integrated into a monolithic and small-footprint device.144 Microfluidic reactors can also be classified into single-phase and two-phase reactors (Figure 4a and b). Single-phase reactors provide synthetic flexibility and can withstand high flow rates.145 More importantly, these reactors allow injection of additional reagents into multi-step reactions and facilitate the formation of more complex structures (Figure 4c). 146-148 However, two main important issues affect the performance of single-phase microfluidic reactor systems: the parabolic velocity profile toward the


Page 12 of 72

Page 13 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


cross-section of the channel and the interaction of the flowing liquid with the inner walls, which generates residence time distributions and reduces the lifetime of the reactor.149 To avoid these problems, two-phase reactors were proposed along with the use of an additional immiscible fluid/gas, which eradicated fouling and elongated the reactor lifetime.148,150 During injection of the immiscible gas or liquid, discrete “droplets” or “slugs” are created. The droplet flow system reduces dispersion and prevents contact with the channel wall.144 Syringe pumps, a mixer, an online absorbance detector, and PL modules are the major constituents of the microfluidic system. Syringe pumps are small in size and used to infuse the fluid. In the microfluidic system, syringe pumps are used to inject the reagents as precursors into the microchannels. The syringe pumps consist of (i) stepper motor, (ii) pusher block, and (iii) syringe holder. The motor drives the plate and accelerates the plunger to release the reagents/fluids from the syringe. In the continuous flow system, two syringes are used: one pulls liquid while the other pushes liquid. Considering their high accuracy, modern syringe pumps are programmed and equipped with a computer connection to record the infusion history. Besides, pumps with an adjustable syringe holder are highly versatile in their applications. Syringe pumps can operate under different ranges of injection volume, such as micro, nano, and pico, with very high delivery precision without the pulseless flow. Flow parameters can be optimized in advanced syringe pumps. For instance, a pressure control system improves the handling of liquids with a high viscosity when fluids are introduced under high pressure. To control temperature, syringe heaters or preheated syringes are utilized. Some syringe pumps allow users to switch between different syringes to regulate the working range.151 In the microfluidic system, sample mixing, which



accelerates the diffusion effect between the flowing liquids and species, is another important parameter. Microfluidic mixers can be divided into two types: active and passive. In general, an external energy force with various forms was applied in active micromixers to dazzle the sample species. This force can come from various sources including magnetic microstirrer,152-154 ultrasonic micromixer,155 pressure perturbation micromixer,147 or electrokinetic micromixer.156 In passive microfluidic mixers, the integration of an external energy source is not required. In addition, the integration of passive mixers into a complex microfluidic system is very easy and does not require complicate technologies. A specially designed microchannel is used for mixing which is categorized into four major types including diffluence micromixer,157 T-type micromixer,158 chaotic micromixer,159 and injectable micromixer. 160 On-line or in-line analytical techniques are used to probe realtime information on the progress of a reaction. From this information, the reaction parameters can easily be altered to obtain products with high yield and quality.161 Integration of in-line optical characterization techniques with microfluidic devices is very easy because of the noninvasive nature of these devices. Fluorescence and absorption detectors provide useful and instantaneous information on the surface uniformity and size distributions of nanocrystals. In situ characterization through fluorescence spectroscopy is a powerful tool for assaying QDs. The obtained fluorescence spectrum (e.g., band emission, FWHM) can be used to calculate the average size and size distribution of the synthesized QDs.144 Hence, fluorescence and absorption techniques are frequently used in the microfluidic synthesis platform for real-time study. A chip-based microfluidic reactor based on an adapted fluorescence detector was reported by Chan et al.162 The group extended their basic idea to a two-phase format to eliminate residence time distributions.163


Page 14 of 72

Page 15 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Lignos et al. 142 integrated fluorescence and absorbance spectrometers into a droplet-based microfluidic system. Here, the optical fiber was connected to the spectrometer situated orthogonal to the incident radiation (Figures 4d–e). The authors also used the combination of deuterium and a halogen lamp for absorbance measurements. 3.1. Microfluidic synthesis of II-VI type cadmium based QDs. The Cd series of QDs, including CdSe and CdS, remain the most widely developed QDs to date due to two decades of research. Consequently, the Cd series of QDs was the first type of QDs to be studied in microfluidic synthesis. In 2002, Nakamura et al.164 first reported the preparation of CdSe nanocrystals in a micro-flow-reactor using Cd(CH3COO)2 as a Cd precursor. In this report, a syringe pump was applied to pump the reaction solution into an oil bathheated silica glass capillary to react with CdSe nanoparticles, as shown in Figure 5a. This system could easily achieve the required temperature to control particle diameters and enabled the reproducible preparation of the desired products. Interestingly, the absorbance peaks of the synthesized product varied from 450 to 600 nm with respect to the particle size of about 2 to 4.5 nm. One year later, Yen et al.165 designed a continuous-flow microcapillary reactor for preparing different sizes of CdSe nanocrystals. As shown in Figure 5b, the Cd and Se precursors were separated into two syringe pumps to control the flow rate of each precursor. The authors prepared the Cd precursor solution by mixing and heating the 0.5 mmol Cd(OH)2, 350 µL (1.1 mmol) oleic acid, and 9 mL squalene. Two of the precursors were pumped individually into a convective mixer to achieve a mixture before flowing into the heated glass micro-tubing. By controlling the ratio of precursors and reaction temperature, a series of CdSe nanocrystals with different particle sizes ranging from ~2.2 to 2.8 nm and emitting different colors, were successfully synthesized.



In the same year, Wang et al.166 reported the microfluidic synthesis of CdSe@ZnS core-shell-structured composite nanoparticles. As shown in Figure 5c, the CdSe precursor was pumped into the first reactor to obtain the CdSe core. Then, the CdSe core was mixed with the ZnS precursor in a Y-mixer before flowing into the second reactor for the coating reaction. This work revealed that continuous synthesis using the proposed microfluidic system was a facile and efficient way to prepare core-shell-structured QDs. Nakamura et al.167 used a microfluidic system for CdSe QD growth and discussed the growth kinetics and PL analysis of the resulting CdSe nanocrystals. The results of this research showed the efficiency of the proposed method for quickly analyzing nanocrystal synthesis and commercial large-scale production of CdSe nanocrystals using the same system as the first report two years ago by Nakamura et al. 164 Later, Wang et al.168 successfully synthesized highly luminescent CdSe@ZnS nanocrystals by using a single molecular ZnS source such as diethyldithiocarbamic acid zinc salt (C2H5NCSS)2Zn) in a microfluidic reactor. This research simplified the microfluidic system to only one syringe pump to push the mixed precursor, as shown in Figure 5d. A PLQY of above 50% and FWHM of approximately 32 nm were obtained from the CdSe@ZnS products synthesized using the microreactor. This research utilized a micro-tube as the reactor to synthesize CdSe QDs. The thickness of the ZnS varied when varying the residence time. At 14s residence time two monolayers of ZnS formed and three monolayers formed at 28s. The authors assuming that the size of the CdSe@ZnS about 5 nm. Besides, the PLQY increased gradually from 14% to 70% when increasing the reaction time up to 28s. However, the PLQY decreased when increasing the residence time more than 28s. Shestopalov et al.169 first discussed the use of a chip-type microreactor to achieve CdS QDs. A buffer solution was used to separate the


Page 16 of 72

Page 17 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


drops of mixed precursors, as shown in Figure 6a, to ensure that the different precursors mixed thoroughly. Yen et al.170 studied a chip-type microfluidic reactor, as shown in Figure 6b. In this work, the authors used gas as a buffer layer to separate the precursor droplets. This reactor shortened the reaction time to control the particle size of the resulting CdSe QDs in contrast to single-phase devices that required long reaction times. In a single phase flow, residence time distribution dependence with flow rate. Conversely, the residence time distribution does not have such a strong flow-rate dependence in the segmented case. Hence, the reaction time was shortening the reaction time in the droplet based chip-type microreactor. Marre et al.171 presented a microfluidic system for the supercritical continuous synthesis of CdSe QDs with narrow size distribution. Figure 6c shows the proposed system for continuous flow and addition of nitrogen as the protecting gas. The use of supercritical hexane in this research led to a higher supersaturation than that achieved by squalene, thereby narrowing the size distribution of the resultant CdSe QDs. In 2015, Naughton et al.172 first reported the high-temperature continuous flow synthesis of CdSe@CdS@ZnS core-shell structured QDs. This research achieved quantum yields of up to 60% by overgrowing an alloy shell on the CdSe QDs through one-step synthesis. On the other hand, PbS and PbSe colloidal QDs also fell in the type of II-VI group. Pan et al.173 developed the dual-temperature-stage coil-reactor system for the synthesis of PbS QDs. Whereas, the high quality QDs synthesized by separating the nucleation and growth process using two-stage reactor system. For this synthesis, the authors utilized the commercially available continuous flow reactor such as FlowSyn Multi-X system (Uniqsis Ltd., Cambridge UK). For the nucleation process, the reactor temperature varied from 80 to 150° C while 50 and 100° C for growth. Compare with batch



and single stage flow reactors, the dual stage flow reactor exhibited high PLQY about 50.6%. In addition, the authors fabricated the photovoltaic device using the PbS QDs synthesized in the dual-stage flow reactor. Fascinatingly, the fabricated device displayed a short circuit current density of 17.88 mA/cm2, solar power conversion efficiency of 4.1% and fill factor of 46% with an open circuit voltage of 0.53 V. Later in the year of 2014, Lignos et al.174 reported the microfluidic synthesis of monodisperse NIR emitting PbS and PbSe QDs using controlled droplet-based microfluidic platform. Notably, the microfluidic system was integrated with in-line fluorescence detection for the real-time assessment of the synthetic process. The authors synthesized the high quality PbS QDs with the emission range from 765−1600 nm and the PLQY was achieved about 28%. Additionally, PbSe QDs with emission wavelength ranging from 800-1600 nm also produced using the same microfluidic platform. Furthermore, the authors used the as-prepared PbS QDs for the fabrication of Schottky solar cells. 3.2. Microfluidic synthesis of III-VI type QDs. Group III–V materials are considered potential alternatives to Cd-based QDs because of their low toxicity. The toxicity of the Cd and In based semiconducting colloidal QDs were studied by Brunetti et al. 175 For this study, the mercaptopropionic acid capped InP/ZnS and CdSe/ZnS QDs were selected to compare the effect of In3+ and Cd2+ release. Whereas, CdSe/ZnS QDs were shown to induce oxidative stress, cell mortality and raised intracellular Ca2+ content in two cell types, while InP/ZnS NCs did not. Later, Chibli et al.176 demonstrated that the generation of reactive oxygen species which inducing cytotoxicity was remarkably lower in the case of InP/ZnS QDs rather than CdTe/ZnS QDs. On account of this results, InP based QDs considered as a potential alternative to high toxic Cd-based quantum dots.


Page 18 of 72

Page 19 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


However, the synthesis of III–V systems presents great challenges due to the bonding nature of the constituent atoms. A strong covalent nature affects the formulation of labile precursor materials, leading to final products with crystal defects. Most primary III–V synthesis techniques follow the proven II–VI synthesis route, which frequently involves high temperatures in the coordinating solvents. Nonetheless, these techniques produce QDs with poor emission and broad size distributions. These problems were rectified by the introduction of synthesis routes based on non-coordinating solvents, which yielded highquality III–V QDs.177 Indium phosphide (InP) is an extensively studied III−V semiconductor with a Bohr exciton radius of ∼10 nm and a low band gap of 1.35 eV. When the sizes of the III–V nanocrystals are varied, their PL properties also vary from the blue (∼480 nm) to the NIR (∼750 nm) regions. Consequently, these materials have attracted attention for their potential applications, including biological imaging and optoelectronics. The major drawback of InP QDs, however, is their poor QE due to surface oxidation. Hence, researchers have developed various approaches, including the synthesis of core–shellstructured and doped InP QDs, to alleviate the aforementioned problems and improve product quality to levels comparable with those of well-established II-VI and IV-VI QDs.24 Various studies have reported the synthesis of core–shell-structured InP QDs. Jo et al. 178 reported the synthesis of multi-shelled InP QDs with a high QE of 82% through hotinjection synthesis. Nightingale et al.177 first reported the microfluidic synthesis of InP QDs in the year of 2009. In this report, two devices, namely, a single capillary and a y-shaped microfluidic device (Figure 7a), were used to synthesize InP QDs. In the single capillary device, the premixed precursor solution was injected using single syringes driven by Harvard



PHD2000 syringe pumps into a glass capillary submerged in an oil bath to heat the solution. The device was integrated with a glass flow-cell connected to a 355 nm diode-pumped HeCd laser and a fiber-optic-coupled CCD spectrometer to monitor product formation. The drawback of this device is its isocratic flow. Moreover, the precursor concentrations cannot be controlled or varied to synthesize QDs with good quality. Hence, the authors designed a y-shaped microfluidic device. Here, a two-in/one-out y-shaped glass microfluidic chip reactor was designed (~300 °C) to enable variation of the indium and phosphorous concentrations. The Y-shaped reactor produced InP nanocrystals with a weak tail in their emission peaks. In 2011, Baek et al.179 developed a microfluidic reactor consisting of three stages, namely, mixing, aging, and sequential injection (Figure 7b). Two kinds of mixing rectors such as uniform and gradient temperature microreactors were utilized for the synthesis of InP QDs (Figure 7c). During synthesis, three syringe pumps (PHD Ultra Hpsi programmable, Harvard apparatus PHD 22/2000 Hpsi, and PHD Ultra) were utilized for solution injection. Stainless steel (Type-316) was used to fabricate the tubes and devices, and multipurpose aluminum-based heating cartridges were used. Using this highpressure/high-temperature microfluidic system, high-quality InP QDs were produced within two minutes. However, the synthesis of core-shell structures is not possible in the developed microfluidic system. One year later, Kim et al.180 developed a device to synthesize core-shell-structured InP/ZnS QDs. The authors maintained the flow rate at approximately 1 mL/min, which is 100 times higher than that applied in the conventional microfluidic technique. In the proposed method, three hydraulic pumps were used to pump the core and shell precursors from flasks. Two furnaces were also used to heat the reaction mixture: one to synthesize


Page 20 of 72

Page 21 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the core and another to synthesize the shell. By optimizing the flow rate and temperature, the scholars successfully synthesized InP/ZnS QDs of four different colors, including bluish green, yellow, orange, and red, and the QYs of the corresponding QDs were approximately 20%, 42%, 34%, and 37%, respectively. The authors demonstrated the application of synthesized QDs to white LEDs. Unfortunately, this technique cannot be used to monitor nanocrystal growth due to the absence of online characterization. In 2015, Ippen et al.181 reported a synthesis technique for producing high-quality InP QDs in a continuous flow reactor using toluene as a solvent. This flow reactor system contained an HPLC pump (Kontron Instruments 322 System) used to transport the reaction mixture and solvent. Similar to the aforementioned reports, stainless steel tubes were used in the flow reactor. The use of toluene in a flow reaction system provides an opportunity to produce large amounts of QDs. However, the QY of the resultant InP products did not increase compared with those obtained from batch systems and continuous-flow devices. Baek et al. 182 reported the synthesis of core-shell QDs using a microfluidic system. This work was a continuation of their previous work on InP cores.179 In this study, the authors synthesized InP/ZnS, InP/ZnSe, InP/CdS, and InAs/InP QDs using chip reactors. Six chip reactors for mixing, aging, the sequential growth of the core and two shells, and annealing, were connected (Figure 7d). The shell rector had a main channel and subchannels. To prevent backflows, each side channel had a flow resistance of 40–60 times higher than that of the main channel. The shell thickness plays an important role in the PL property of the core–shell-structured InP QDs. Baek et al. designed a silicon–Pyrex chip reactor with sub-channels to control the formation of the shell and restrict the secondary nucleation of shell particles at various temperatures and injection profiles. Besides, the



authors varied the absorption and emission wavelength of InP QDs by varying the shell thickness. Hence, the red-shift observed in the corresponding absorption and PL peaks of the final product (Figure 7e). Besides these features, the microfluidic platform was enabled with an inline UV-vis measurement device, which helped monitor nanocrystal quality. A SD2000 fiber optics spectrometer connected to an Ocean Optics DH-2000 was used as a light source. The quality of the different III–V type core-shell structures synthesized was comparable with those obtained from conventional batch synthesis. 3.3. Microfluidic synthesis of I-III-VI type QDs. Similar to the QDs based on IIIV group elements, group I-III-VI QDs have received attention for their potential ability to replace Cd- and Pb-free QDs. For instance, CuInS2, CuInSe2, AgInS2, and Cu2ZnSnS4 QDs have been reported to be useful for various potential applications, including solar cells, QLEDs, and bioimaging. 183 The PL properties of these QDs can be tuned from the visible to the NIR regions.184 However, these materials exhibit poor PLQY due to the formation of defects. Hence, ZnS with a large band gap is used to passivate their surfaces to yield a high PLQY of up to 80%.185-187 The large-scale synthesis of CuInS2/ZnS semiconducting nanocrystals was reported by J. Lee and Han in 2014.188 In their work, hydraulic pumps were used to transport the reaction solution from the flask to the furnace (Figure 8a). This instrument set-up was based on the report published by Kim et al.180 and used to synthesize InP/ZnS QDs. The group obtained core–shell-structured CuInS2/ZnS with a PLQY of 61.4%. In 2013, Li et al. 189 developed the continuous flow technique to synthesize Ag–In– Zn–S/ZnS and Cu–In–Zn–S/ZnS core-shell QDs. In this technique, the premixed solution was injected through a syringe pump connected to a stainless steel needle (1:6 × 400 mm).


Page 22 of 72

Page 23 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


To ensure completion of the reaction, the scholars encased the stainless-steel tubing with heating tape that was approximately 15 cm in length and maintained the reaction temperature at 230 °C. The residence time was varied according to the flow rate. After heating, the core portion was collected in a centrifuge tube to which a premixed shell precursor solution had been added. This solution was then transferred to the heating zone by using another syringe pump. The authors observed that a decrease in flow rate can cause aggregation due to the long residence time in the heating zone. Conversely, high flow rates enhance the size distribution of the resultant products. Using their homemade continuous flow system, the researchers synthesized Cu–In–Zn–S/ZnS and Ag–In–Zn–S/ZnS QDs, emitting different colors, with PLQY of above 40%. However, a major drawback of this system is that the core and shell reactors were not connected serially, and manual injection of the shell precursor into the core affected the shell growth and thickness. Three years later, Yashina et al.183 developed an advanced two-step droplet-based microfluidic platform to synthesize CuInS2/ZnS QDs. Considering the interaction of reaction mixtures with the microfluidic channel inner wall, the authors designed a droplet-based microfluidic system that suppressed secondary nucleation. Figure 8b shows a schematic of this microfluidic system. Precision syringe pumps (neMESYS Low Pressure Syringe Pumps, Cetoni GmbH, Germany) were utilized to inject reagents for initial mixing via the T mixer. All syringe pumps were connected to a polyether ether ketone (PEEK) polytetrafluoroethylene (PTFE) tubing (ID 250 mm, OD 1/1600, Upchurch Scientific, Germany). The microfluidic system was enabled with an inline optical detection system. In general, real-time optical detection is achieved before the collection point. In this system, the authors installed the optical detection system after core and core-shell synthesis to help to monitor the reaction



parameters before and after the addition of the shell material. The authors used a UV LED (M405L2-UV Mounted LED, 1000 mA, 410 mW, Thorlabs, Germany) as an excitation source. In their work, they synthesized core-shell CuInS2/ZnS with a high PLQY yield of approximately 55% and high production yield. By varying the reaction parameters, the researchers obtained a highly stable core-shell-structured CuInS2/ZnS with different emission wavelengths ranging from 580–760 nm. 3.4. Microfluidic synthesis of perovskite QDs. Perovskite QDs have recently drawn attention because of their unique properties, such as narrow FWHM, high QE, and widely tunable emission. PQDs have the general formula AnBX2+n, where A (monovalent cation) = Cs, FA, MA; B (divalent cation) =Pb; and X (monovalent anion) = Cl, Br, I. Protesescu et al.190 synthesized different lead halide perovskite QDs by the hot injection method after working on the development of a microfluidic platform to study their reaction kinetics. Lignos et al.191 first reported a microfluidics platform to synthesize perovskite nanocrystals integrated with online detection absorbance and fluorescence properties (Figure 9a). In the experimental design, syringe pumps were used to inject dispersed-phase carrier fluids through PEEK cross junctions and a PTFE tubing for connection in different segments. Online absorbance measurement was carried out using a halogen lamp (HL-2000 HP, Ocean Optics, UK) as an illumination source. Then, the output beam collimated (F230SMA-C, Thorlabs, Germany) and oriented toward the flow direction by using a plano-convex cylindrical lens (LJ4709RM, Thorlabs, Germany). For online PL measurements, the authors used a blue LED (M405L2-Mounted LED, Thorlabs, Germany) as an excitation source and a collimated beam through a dichroic beam splitter (Multiphoton LP-Strahlenteiler HC 405 LP, AHF, Germany), focusing on an aspheric lens


Page 24 of 72

Page 25 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(A240TM – f = 8.0 mm – NA 0.50, Thorlabs, Germany). To synthesize perovskite QDs, the precursor was loaded into the syringe pumps, mixed rapidly at different cross junctions (R1 and R2), and formed into a droplet, which was heated at different reaction temperatures for nuclear formation and growth. In this complete process, several important factors, such as reaction temperature and R1 (Pb/Cs) and R2 (Br/Cl and I/Br) ratio, were varied to promote nucleation of QDs. The same group used a microfluidic system to conduct a kinetic study on FAPbBr3, FAPbI3, and FAPb(Br/I)3. Maceiczyk et al.192 hypothesized that, during the formation of FAPb(Br/I)3, synthesis of CsPbI3 first occurs followed by the Br reaction. This group extended their study to use an online automated droplet microfluidics system and form blue emitting FAPb(ClXBr1-X)3. Figure 9b shows the microfluidic experimental system used to synthesize nanoplatelets and nanocubes. A systematic variation was applied to the synthesis process, and the temperature was changed from 25 °C to 150 °C with a constant ratio of Fa/Pb and Br. Through this method, the authors observed that the FWHM was reduced at 130 °C but broader at low-reaction temperatures. In a recent article on the large-scale production of multinary perovskites, Ligons et al.193 used an automatic microfluidics platform for the synthesis of CsXFA1-X (Br1-YIY)3 in the PL region of 700–800 nm, as shown in Figure 9c. CsXFA1-X (Br1-YIY)3 was used as an emissive layer in the LED approach with an EQE of 5.9% at 0.1 mA cm-2. Ligons et al.194 developed an online measurement microfluidic system and synthesized different types of lead halide perovskite QDs with tunable halide emission. Several other groups also reported the development of microfluidic systems to synthesize novel materials related to perovskite QDs. Ma et al.195 used a 1D–2D microfluidics spinning reactor to synthesize lead halide perovskite QDs embedded into poly-(methyl methacrylate) (PMMA) to



develop WLEDs. In the first step of the synthesis process, Cs+ and Pb+2 with PMMA in chloroform were spin-coated onto a glass film. Then, the precursor Br- was combined with a PMMA flow under a stable voltage and constant flow rate, simultaneously microfiber form having Cs+ and Pb+2 ions with Br– convert into fluorescent CsPbBr3 embedded into the PMMA. This method could be used to form different composites with core-shell structures for the possible synthesis of perovskites with stable structures. Song et al.196 applied the Couette–Taylor flow method to synthesize perovskite QDs. This method was previously used to synthesize graphene oxide (Figure 9d). In this method, the precursor solution is introduced into the gap between two coaxial cylinders and the inner cylinder rotates at a constant speed of approximately 1000 rpm. The XRD spectrum of the products confirmed the presence of single-phase rhombohedral crystals of the Cs4PbBr6 system. Bao et al.197 recently developed a home-made continuous microfluidics flow system to synthesize Cs4PbBr6 microcrystals for white LED applications. In this work, the scholars varied the reaction temperature from 60 °C to 150 °C and observed that the PL intensity and quantum yield increased with increasing temperature. They also observed that dimethyl sulfoxide washing is effective rather than tert-butyl alcohol with reference to PL intensity. Table-1 shows the comparison table of the different microfluidic system used for the microfluidic synthesis of different types of QDs. 4. CONCLUSIONS AND FUTURE OUTLOOK In summary, semiconductor colloidal QDs are promising potential alternatives to conventional QDs in the field of LED and biomedical applications. Considering the toxicity of Cd- and Pb-based QDs, the development of non-toxic QDs with high QE has gained remarkable research attention. In particular, group III–V and perovskite QDs have


Page 26 of 72

Page 27 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


respectively been extensively studied for biomedical and QLED applications. However, the quality of these materials has not reached that of Cd-based QDs. New developments have been achieved in the batch reactor systems to improve the QE, stability, brightness, and EQE of semiconductor colloidal QDs. The major achievement thus far involves the synthesis of core–shell-structured QDs. QDs with a thick outer shell exhibit higher PL properties than do thin-shelled QDs. In addition, changing the elemental composition of the buffer layer shifts the emission wavelength of QDs. Despite these improvements, however, controlling the reaction parameters when scaling up the reaction is difficult. Hence, microfluidic systems have been adapted to synthesize QDs. After the first report in 2002, a number of research groups applied the microfluidic platform to synthesize different types of QDs. Over the last 16 years, many key innovations have been introduced to improve the performance of microfluidic systems. For instance, multi-phase flow reactors have been utilized to resolve flow issues and improve reactor stability. More importantly, in situ characterization of nanocrystals has been integrated into these systems for real-time product evaluation. Inline optical characterization helps control the reaction parameters, such as temperature, residence time, and reagent concentration. By controlling these parameters, QDs with the desired emission wavelength and narrow size distribution can be synthesized. Most microfluidic systems today are enabled with only absorbance and fluorescence capabilities. However, integration of other characterization techniques, such as in situ TEM, quantum yield analysis, and time-correlated single photon counting, may help synthesize high-quality products. The major issue in these systems is their inability to synthesize core-shell–shell-structured III–V QDs. Thus far, the microfluidic system has



only been used to synthesize core-shell structures. Controlling the shell thickness is a major task in the synthesis of InP- and InAs-based core–shell-structured QDs. Synthesis of a buffer layer with an alloyed composition is also a challenging task. P(TMS)3, as a highly reactive phosphorous precursor, was used to synthesize high-quality InP QDs with high yield. However, storage of P(TMS)3 at room temperature is very difficult. Hence, a special design is required to store and use this precursor in microfluidic systems. Another problem in the synthesis of III–V QDs is channel fouling due to the interaction of reagents with the channel wall. Droplet-based microfluidic systems can alleviate this problem, but this system has not been utilized to synthesize III–V QDs. As well, integration of optical characterization with the synthesis of core, core-shell, and core-shell–shell structures can help synthesize III–V QDs with emission ranges above 650 nm for biological applications. For future work, the microfluidics approach could be applied to the synthesis and understanding of the kinetics of doped perovskite QDs, Pb-free perovskites, and core– shell-structured perovskite QDs. In addition, the large-scale synthesis of QDs is expected to advance the development of semiconductor nanocrystals in display and biomedical applications. In comparison with previously published review articles, the present review discusses the applications of QDs and developments in microfluidic platforms for QD synthesis. ACKNOWLEDGMENTS This work was financially supported by the Advanced Research Center of Green Materials Science and Technology from The Featured Area Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education


Page 28 of 72

Page 29 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(107L9006) and the Ministry of Science and Technology in Taiwan (Contracts MOST 1072113-M-002-008-MY3 and MOST 107-3017-F-002-001).



Figure captions Table-1: Comparison table of the different microfluidic system used for the microfluidic synthesis of different types of QDs. Figure 1: (a) Future applications of wearable and flexible displays. Reprinted with permission from ref 56. Copyright © 2018, Springer Nature. (b) Size-dependent emission of CdSe QDs covering the entire visible light range. Reprinted with permission from ref 77. Copyright 2010 John Wiley and Sons. (c) Commission Internationale de Eclairage (CIE) chromaticity diagram exhibit the color gamut of CdSe QDs. Reprinted with permission from ref 56. Copyright © 2018, Springer Nature. (d) Charge carrier dynamics of core– shell-structured QDs containing thin and thick shells. Reprinted with permission from ref 64. Copyright © 2012, Springer Nature. (e) Time-resolved PL spectra obtained from QDs under different conditions. The inset reflects the change in carrier lifetime with respect to voltage. (f) Comparison of the EQEs of QLEDs with a core-shell structure and different compositions of CdSe/CdS/Zn0.5Cd0.5S and CdSe/CdS QDs. Both Reprinted with permission from ref 65. Copyright © 2013, Springer Nature. (g, h) Current densityluminance-voltage characteristics of QDs. Comparison of (g) the current efficiencies and (h) EQEs of QLEDs containing CdSe/ZnS QDs featuring CdS-rich (blue) and ZnSe-rich (red) intermediate shells. Both Reprinted with permission from ref 66. Copyright © 2015, Springer Nature. (i) Schematic diagram, energy band diagram, and TEM images of double heterojunction nanorods. Reprinted with permission from ref 67. Copyright © 2014, Springer Nature. (j) EL spectrum of flexible InP@ZnSeS QLEDs on a polyethersulfone substrate. Reprinted from ref 73. Copyright 2013 American Chemical Society. (k) Schematic and TEM images of core–shell-structured Cu–In–S/ZnS QDs. (l) EL spectra of


Page 30 of 72

Page 31 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Cu–In–S/ZnS QLEDs as a function of applied voltage. Both Reprinted from ref 79. Copyright 2013 American Chemical Society. Figure 2: Applications of semiconducting colloidal QDs. Figure 3: (a) NIR spectral region for bioapplications. Reprinted from ref 114. Copyright 2013 American Chemical Society. (b) Plot of the extinction coefficients of oxy- and deoxyhemoglobin and water against the visible to NIR wavelengths. Reprinted from ref 115. Copyright 2013 American Chemical Society. (c) Bioimaging application of CuInS/ZnS QDs. Reprinted from ref 120. Copyright 2013 American Chemical Society. Figure 4: (a) Schematic of single- and (b) two-phase flow reactors containing T- and Yjunctions, respectively. Both Reprinted with the permission from ref 144. Copyright 2017 Royal Society of Chemistry. (c) Schematic of the microfluidic system developed by Toyota et al. Reprinted from ref 148. Copyright 2013 American Chemical Society. (d) Image of a microfluidic system enabled with inline absorbance and PL modules. (e) Image of an inline fluorescence detection system. Both Reprinted from ref 142. Copyright 2013 American Chemical Society. Figure 5: (a) Diagram of a flow reactor for CdSe nanoparticles Reprinted with the permission from ref 164. Copyright 2002 Royal Society of Chemistry. (b) Schematic of a capillary reactor. Reprinted with permission from ref 165. Copyright 2003 John Wiley and Sons (c) Schematic illustration of a multi-step continuous synthesis system. Reprinted with the permission from ref 166. Copyright 2004 Royal Society of Chemistry. (d) Schematic representation of a flow reactor for CdSe nanoparticles. Reprinted with permission from ref 168. Copyright 2005 John Wiley and Sons.



Figure 6: (a) Micrograph of a microfluidic device for performing droplet-based, two-step synthesis with millisecond-scale time control. Reprinted with the permission from ref 169. Copyright 2004 Royal Society of Chemistry. (b) Reactor with a thermally isolated heating zone region and cooled outlet zone. Reprinted with permission from ref 170. Copyright 2005 John Wiley and Sons. (c) Experimental setup featuring a high-pressure hightemperature microreactor, a compression-cooling aluminum part, a high-pressure syringe pump, a five-way high-pressure valve, and a high-pressure reservoir containing four vials. Reprinted with permission from ref 171. Copyright 2008 John Wiley and Sons. Figure 7: (a) Schematic of single capillary and Y-shaped microfluidic devices used to synthesize InP QDs. Reprinted from ref 176. Copyright 2011 American Chemical Society. (b) Microfluidic reactor consisting of three stages, namely, mixing, aging, and sequential injection. (c) Uniform- and gradient-temperature mixing microreactors. Both Reprinted with permission from ref 179. Copyright 2011 John Wiley and Sons. (d) Illustration of a multistage microfluidic platform to synthesize InP/ZnS core/shell QDs. (e) Absorption and emission spectra of the InP/CdS QDs. Both Reprinted with permission from ref 182. Copyright 2018 John Wiley and Sons. Figure 8: (a) Schematic diagram of a hybrid flow reactor used to synthesize CuInS2/ZnS. Reprinted with permission from ref 188. Copyright © 2014, Springer Nature. (b) Schematic of a two-stage droplet-based microfluidic system used to synthesize CuInS2/ZnS NCs. Reprinted with the permission from ref 183. Copyright 2016 Royal Society of Chemistry Figure 9: (a) Schematic microfluidics platforms diagram for synthesize different lead halide (CsPbX3, X = Cl, Br, I, Cl/Br and Br/I) PQDs. Reprinted from ref 191. Copyright


Page 32 of 72

Page 33 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2016 American Chemical Society. (b) Microfluidics platforms diagram used with integrated segmented flows with online PL and absorbance for FAPbCl3 and FAPb(ClX/Br1-X)3 PQDs. Reprinted from ref 192. Copyright 2017 American Chemical Society. (c) Schematic microfluidics device with different segments for synthesizing CsXFA1-XPb(BrX/I1-X)3 PQDs. Reprinted from ref 193. Copyright 2018 American Chemical Society. (d) Couette–Taylor apparatus used to synthesize Cs4PbBr6 microcrystals. Reprinted with permission from ref 196. Copyright © 2018, Springer Nature.



Page 34 of 72

Table 1 Nanocrystal

Reactor system

CdSe

Silica class capillary

Inline optical characterization Enabled/Disabled Disabled

PLQY

Ref.

Not reported

164

Disabled

Not reported

165

Disabled

Not reported

166

Disabled

>10%

167

Disabled

16%

181

Enabled

40 % at 554 nm

182

reactor InP/ZnS

Multistage chip microreactor

CuInS2/ZnS

32% at 630 nm

Hybrid flow reactor

Disabled

61.4%

188

Disabled

40%

189

Enabled

55%

183

Enabled

Not reported

191

Enabled

Not reported

192

Enabled

Not reported

193

Enabled

Not reported

194

formed by serial connections of both batch and continuous processes AgInZnS/ZnS

Continuous-flow reactor

CuInS2/ZnS

Two-stage dropletbased microfluidic reactor.

CsPbX3

Droplet-based microfluidic reactor

FAPbBr3


FAPb(Cl1−x Brx)3


CsxFA1–x PbI3

Droplet-based microfluidic reactor 35

ACS Paragon Plus Environment


CsPbBr3/ PMMA

Microfluidic spinning

Page 36 of 72

Disabled

45%

195

Disabled

46%

196

Disabled

24%

197

microreactors Cs4PbBr6

CouetteTaylor fow reactor

Cs4PbBr6



Page 37 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1



Figure 2


Page 38 of 72

Page 39 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3



Figure 4


Page 40 of 72

Page 41 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5



Figure 6


Page 42 of 72

Page 43 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7



Figure 8


Page 44 of 72

Page 45 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 9



REFERENCES 1.

Dai, X.; Deng, Y.; Peng, X.; Jin, Y. Quantum‐Dot Light‐emitting Diodes for Large‐Area Displays: Towards the Dawn of Commercialization Adv. Mater. 2017, 29, 1607022.

2.

Zhou, J.; Yang, Y.; Zhang, C.Y. Toward Biocompatible Semiconductor Quantum Dots: from Biosynthesis and Bioconjugation to Biomedical Application Chem. Rev. 2015, 115, 11669−11717.

3.

Pu, Y.; Cai, F.; Wang, D.; Wang, J. X.; Chen, J. F. Colloidal Synthesis of Semiconductor Quantum Dots Toward Large-scale Production: A review Ind. Eng. Chem. Res. 2018, 57, 1790−1802.

4.

Resch-Genger, U.; Grabolle, M.; Cavaliere-Jaricot, S.; Nitschke, R.; Nann, T. Quantum Dots Versus Organic Dyes as Fluorescent Labels Nat. Methods 2008, 5, 763−775.

5.

Michalet, X.; Pinaud, F.; Bentolila, L.; Tsay, J.; Doose, S.; Li, J.; Sundaresan, G.; Wu, A.; Gambhir, S.; Weiss, S. Quantum Dots for Live Cells, In Vivo imaging, and Diagnostics Science 2005, 307, 538−544.

6.

Chen, X.; Nazzal, A. Y.; Xiao, M.; Peng, Z. A.; Peng, X. Photoluminescence from Single CdSe Quantum Rods J. Lumin. 2002, 97, 205−211.

7.

Qu, L.; Peng, Z. A.; Peng, X. Alternative Routes Toward High Quality CdSe Nanocrystals Nano Lett. 2001, 1, 333−337.

8.

Qu, L.; Yu, W. W.; Peng, X. In-situ Observation of the Nucleation and Growth of CdSe Nanocrystals Nano Lett. 2004, 4, 465−469. 46 ACS Paragon Plus Environment

Page 46 of 72

Page 47 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


9.

Wang, X.; Qu, L.; Zhang, J.; Peng, X.; Xiao, M. Surface-Related Emission in Highly Luminescent CdSe Quantum Dots Nano Lett. 2003, 3, 1103−1106.

10. Yu, W. W.; Peng, X. Formation of High‐quality CdS and other II–VI Semiconductor Nanocrystals in Noncoordinating Solvents: Tunable Reactivity of Monomers Angew. Chem. Int. Ed. Engl. 2002, 41, 2368-2371. 11. Morello, G.; De Giorgi, M.; Kudera, S.; Manna, L.; Cingolani, R.; Anni, M. Temperature and Size Dependence of Nonradiative Relaxation and Exciton−Phonon Coupling in Colloidal CdTe Quantum Dots J. Phys. Chem. C. 2007, 111, 5846−5849. 12. Peng, Z. A.; Peng, X. Formation of High-Quality CdTe, CdSe, and CdS Nanocrystals Using CdO as Precursor J. Am. Chem. Soc. 2001, 123, 183−184. 13. Kolackova, M.; Moulick, A.; Kopel, P.; Dvorak, M.; Adam, V.; Klejdus, B.; Huska, D. Antioxidant, Gene Expression and Metabolomics Fingerprint Analysis of Arabidopsis Thaliana Treated by Foliar Spraying of ZnSe Quantum Dots and Their Growth Inhibition of Agrobacterium Tumefaciens J. Hazard. Mater. 2019, 365, 932−941. 14. Wegner, K. D.; Pouget, S.; Ling, W. L.; Carrière, M.; Reiss, P. Gallium–a Versatile Element for Tuning the Photoluminescence Properties of InP Quantum Dots Chem. Commun. 2019, 55, 1663−1666. 15. Battaglia, D.; Peng, X. Formation of High Quality InP and InAs Nanocrystals in a Noncoordinating Solvent Nano Lett. 2002, 2, 1027−1030. 16. Akdas, T.; Haderlein, M.; Walter, J.; Zubiri, B. A.; Spiecker, E.; Peukert, W. Continuous Synthesis of CuInS2 Quantum Dots RSC Adv. 2017, 7, 10057−10063.



17. Choi, J. W.; Woo, H. C.; Huang, X.; Jung, W. G.; Kim, B. J.; Jeon, S.W.; Yim, S. Y.; Lee, J. S.; Lee, C. L. Organic–Inorganic Hybrid Perovskite Quantum Dots with High PLQY and Enhanced Carrier Mobility Through Crystallinity Control by Solvent Engineering and Solid-State Ligand Exchange Nanoscale 2018, 10, 13356−13367. 18. Lim, J.; Bae, W. K.; Kwak, J.; Lee, S.; Lee, C.; Char, K. Perspective on Synthesis, Device Structures, and Printing Processes for Quantum Dot Displays Opt Mater Express 2012, 2, 594−628. 19. Baskoutas, S.; Terzis, A. F. Size-Dependent Band Gap of Colloidal Quantum Dots J. Appl. Phys. 2006, 99, 013708−0137011. 20. Yao, J.; Yang, M.; Duan, Y. Chemistry, Biology, and Medicine of Fluorescent Nanomaterials and Related Systems: New Insights into Biosensing, Bioimaging, Genomics, Diagnostics, and Therapy Chem. Rev. 2014, 114, 6130−6178. 21. Gao, X.; Yang, L.; Petros, J. A.; Marshall, F. F.; Simons, J. W.; Nie, S. In Vivo Molecular and Cellular Imaging with Quantum Dots Curr. Opin. Biotechnol. 2005, 16, 63−72. 22. Petta, J. R.; Johnson, A. C.; Taylor, J. M.; Laird, E. A.; Yacoby, A.; Lukin, M. D.; Marcus, C. M.; Hanson, M. P.; Gossard, A. C. Coherent Manipulation of Coupled Electron Spins in Semiconductor Quantum Dots Science 2005, 309, 2180−2184. 23. Park, J.; Dvoracek, C.; Lee, K. H.; Galloway, J. F.; Bhang, H. e. C.; Pomper, M. G.; Searson, P. C. CuInSe/ZnS core/shell NIR Quantum Dots for Biomedical Imaging Small 2011, 7, 3148-3152. 24. Tamang, S.; Lincheneau, C.; Hermans, Y.; Jeong, S.; Reiss, P. Chemistry of InP Nanocrystal Synthesis Chem. Mater. 2016, 28, 2491−2506.


Page 48 of 72

Page 49 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


25. Owen, J; Brus, L. Chemical Synthesis and Luminescence Applications of Colloidal Semiconductor Quantum Dots J. Am. Chem. Soc. 2017, 139, 10939−10943. 26. Rafipoor, M.; Dupont, D.; Tornatzky, H.; Tessier, M.D.; Maultzsch, J.; Hens, Z.; Lange, H. Strain Engineering in InP/(Zn, Cd)Se Core/Shell Quantum Dots Chem. Mater. 2018, 30, 4393−4400. 27. Kim, S.; Fisher, B.; Eisler, H. J; Bawendi, M. Type-II Quantum Dots: CdTe/CdSe (Core/Shell) and CdSe/ZnTe (Core/Shell) Heterostructures J. Am. Chem. Soc. 2003, 125, 11466−11467. 28. Wang, L.; Nonaka, K.; Okuhata, T.; Katayama, T.; Tamai, N. Quasi-Type II Carrier Distribution in CdSe/CdS Core/Shell Quantum Dots with Type i Band Alignment J. Phys. Chem. C 2018, 122, 12038−12046. 29. Xu, S.; Ziegler, J.; Nann, T. Rapid Synthesis of Highly Luminescent InP and InP/ZnS Nanocrystals J. Mater. Chem. 2008, 18, 2653−2656. 30. Li, L.; Reiss, P. One-Pot Synthesis of Highly Luminescent InP/ZnS Nanocrystals Without Precursor Injection J. Am. Chem. Soc. 2008, 130, 11588−11589. 31. Xie, R.; Battaglia, D.; Peng, X. Colloidal InP Nanocrystals as Efficient Emitters Covering Blue to Near-Infrared J. Am. Chem. Soc. 2007, 129, 15432−15433. 32. Haubold, S.; Haase, M.; Kornowski, A.; Weller, H. Strongly Luminescent InP/ZnS Core–Shell Nanoparticles ChemPhysChem, 2001, 2, 331-334. 33. Kim, M. R.; Chung, J. H.; Lee, M.; Lee, S.; Jang, D. J. Fabrication, Spectroscopy, and Dynamics of Highly Luminescent Core–Shell InP@ ZnSe Quantum Dots J. Colloid Interface Sci. 2010, 350, 5−9.



34. Lim, J.; Bae, W. K.; Lee, D.; Nam, M. K.; Jung, J.; Lee, C.; Char, K.; Lee, S. InP@ ZnSeS, Core@ Composition Gradient Shell Quantum Dots with Enhanced Stability Chem. Mater. 2011, 23, 4459−4463. 35. Mićić, O. I.; Smith, B. B.; Nozik, A. J. Core−Shell Quantum Dots of Lattice-Matched ZnCdSe2 Shells on InP Cores: Experiment and Theory J. Phys. Chem. B 2000, 104, 12149−12156. 36. Sugunan, A.; Zhao, Y.; Mitra, S.; Dong, L.; Li, S.; Popov, S.; Marcinkevicius, S.; Toprak, M. S.; Muhammed, M. Synthesis of Tetrahedral Quasi-Type-II CdSe–CdS Core–Shell Quantum Dots Nanotechnology 2011, 22, 425202−425208. 37. Park, J.; Kim, S.; Kim, S.; Yu, S. T.; Lee, B.; Kim, S. W. Fabrication of Highly Luminescent InP/Cd and InP/CdS Quantum Dots J. Lumin. 2010, 130, 1825−1828. 38. Zhou, Q.; Bai, Z.; Lu, W.G.; Wang, Y.; Zou, B.; Zhong, H. In Situ Fabrication of Halide Perovskite Nanocrystal‐Embedded Polymer Composite Films with Enhanced Photoluminescence for Display Backlights Adv. Mater. 2016, 28, 9163-9168. 39. Xuan, T.; Huang, J.; Liu, H.; Lou, S.; Cao, L.; Gan, W.; Liu, R. S.; Wang, J. SuperHydrophobic Cesium Lead Halide Perovskite Quantum Dots-Polymer Composites with High Stability and Luminescent Efficiency for Wide Color Gamut White LightEmitting Diodes Chem. Mater, 2019, 31, 3, 1042−1047. 40. Swarnkar, A.; Marshall, A. R.; Sanehira, E. M.; Chernomordik, B. D.; Moore, D. T.; Christians, J. A.; Chakrabarti, T.; Luther, J. M. Quantum Dot–Induced Phase Stabilization of α-CsPbI3 Perovskite for High-Efficiency Photovoltaics Science 2016, 354, 92−95.


Page 50 of 72

Page 51 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


41. Xuan, T.; Yang, X.; Lou, S.; Huang, J.; Liu, Y.; Yu, J.; Li, H.; Wong, K. L.; Wang, C.; Wang, J. Highly Stable CsPbBr3 Quantum Dots Coated With Alkyl Phosphate for White Light-Emitting Diodes Nanoscale, 2017, 9, 15286−15290. 42. Zhang, H.; Wang, X.; Liao, Q; Xu, Z.; Li, H.; Zheng, L.; Fu, H. Embedding Perovskite Nanocrystals Into a Polymer Matrix for Tunable Luminescence Probes in Cell Imaging Adv. Funct. Mater. 2017, 27, 1604382. 43. Xuan, T.; Lou, S.; Huang, J.; Cao, L.; Yang, X.; Li, H.; Wang, J. Monodisperse and Brightly Luminescent CsPbBr3/Cs4PbBr6 Perovskite Composite Nanocrystals Nanoscale, 2018, 10, 9840−9844. 44. Litvin, A. P; Martynenko I. V; Milton, P. F; Baranov, A. V; Fedorov, A. V; Gun'ko, Y. K. Colloidal Quantum Dots for Optoelectronics J. Mater. Chem. A 2017, 5, 13252−13275. 45. Pietryga, J. M; Park, Y. S.; Lim, J.; Fidler, A. F.; Bae, W. K.; Brovelli, S; Klimov, V. I. Spectroscopic and Device Aspects of Nanocrystal Quantum Dots Chem. Rev. 2016, 116, 10513−10622. 46. Xu, C; Poduska, K. M. A Bright Future for Color-Controlled Solid State Lighting J. Mater. Sci.: Mater. Electron. 2015, 26, 4565–4570. 47. Han, M.; Gao, X.; Su, J. Z.; Nie, S. Quantum-Dot-Tagged Microbeads For Multiplexed Optical Coding of Biomolecules Nat. Biotechnol. 2001, 19, 631−635. 48. Rosenthal, S. J; Chang, J. C; Kovtun, O; McBride, J. R; Tomlinson, I. D. Biocompatible Quantum Dots for Biological Applications Chem. Biol. 2011, 18, 10−24.



49. Hu, J.; Wang, Z. Y.; Li, C. C.; Zhang, C. Y. Advances in Single Quantum Dot-Based Nanosensors Chem. Commun. 2017, 53, 13284−13295. 50. Cui, L.; Li, C. C.; Tang, B.; Zhang, C. Y. Advances In The Integration of Quantum Dots With Various Nanomaterials for Biomedical and Environmental Applications Analyst 2018, 143, 2469−2478. 51. Kim, R. H.; Kim, D. H.; Xiao, J.; Kim, B. H.; Park, S. I.; Panilaitis, B.; Ghaffari, R.; Yao, J.; Li, M.; Liu, Z. Waterproof AlInGaP Optoelectronics on Stretchable Substrates with Applications in Biomedicine and Robotics Nat. Mater. 2010, 9, 929−937. 52. Park, S. I.; Xiong, Y.; Kim, R. H.; Elvikis, P.; Meitl, M.; Kim, D. H.; Wu, J.; Yoon, J.; Yu, C. J.; Liu, Z. Printed Assemblies of Inorganic Light-Emitting Diodes for Deformable and Semitransparent Displays Science 2009, 325, 977−981. 53. Han, T. H.; Lee, Y.; Choi, M. R.; Woo, S. H.; Bae, S. H.; Hong, B. H.; Ahn, J. H.; Lee, T. W. Extremely Efficient Flexible Organic Light-Emitting Diodes with Modified Graphene Anode Nat. Photon. 2012, 6, 105−110. 54. Liang, J.; Li, L.; Niu, X.; Yu, Z.; Pei, Q. Elastomeric Polymer Light-Emitting Devices and Displays Nat. Photon. 2013, 7, 817−824. 55. Yang, J.; Choi, M. K.; Kim, D. H.; Hyeon, T. Designed Assembly and Integration of Colloidal Nanocrystals for Device Applications Adv. Mater. 2016, 28, 1176-1207. 56. Choi, M. K.; Yang, J.; Hyeon, T.; Kim, D. H. Flexible Quantum Dot Light-Emitting Diodes for Next-Generation Displays npj Flexible Electronics 2018, 2, 1−14. 57. Pimputkar, S.; Speck, J. S.; DenBaars, S. P.; Nakamura, S. Prospects for LED Lighting Nat. Photon. 2009, 3, 180−182.


Page 52 of 72

Page 53 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


58. Chen, M. H.; Hou, J.; Hong, Z.; Yang, G.; Sista, S.; Chen, L. M.; Yang, Y. Efficient Polymer Solar Cells with Thin Active Layers Based on Alternating Polyfluorene Copolymer/Fullerene Bulk Heterojunctions Adv. Mater. 2009, 21, 4238-4242. 59. Kim, B. H.; Onses, M. S.; Lim, J. B.; Nam, S.; Oh, N.; Kim, H.; Yu, K. J.; Lee, J. W.; Kim, J. H.; Kang, S. K. High-Resolution Patterns of Quantum Dots Formed by Electrohydrodynamic Jet Printing for Light-Emitting Diodes Nano Lett. 2015, 15, 969−973. 60. Talapin, D. V.; Lee, J. S.; Kovalenko, M. V.; Shevchenko, E. V. Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications Chem. Rev. 2009, 110, 389−458. 61. Shirasaki, Y.; Supran, G. J.; Bawendi, M. G.; Bulović, V. Emergence of Colloidal Quantum-Dot Light-Emitting Technologies Nat. Photon. 2013, 7, 13−23. 62. Chen, Z.; Nadal, B.; Mahler, B.; Aubin, H.; Dubertret, B. Quasi‐2D Colloidal Semiconductor Nanoplatelets for Narrow Electroluminescence Adv. Funct. Mater. 2014, 24, 295-302. 63. Bae, W. K.; Char, K.; Hur, H.; Lee, S. Single-Step Synthesis of Quantum Dots with Chemical Composition Gradients Chem. Mater. 2008, 20, 531−539. 64. Galland, C.; Ghosh, Y.; Steinbrück, A.; Hollingsworth, J. A.; Htoon, H.; Klimov, V. I. Lifetime Blinking in Nonblinking Nanocrystal Quantum dots Nat. Commun. 2012, 3, 908−914. 65. Bae, W. K.; Park, Y. S.; Lim, J.; Lee, D.; Padilha, L. A.; McDaniel, H.; Robel, I.; Lee, C.; Pietryga, J. M.; Klimov, V. I. Controlling the influence of Auger recombination



on the performance of quantum-dot light-emitting diodes Nat. Commun. 2013, 4, 2661−2668. 66. Yang, Y.; Zheng, Y.; Cao, W.; Titov, A.; Hyvonen, J.; Manders, J. R.; Xue, J.; Holloway, P. H.; Qian, L. High-Efficiency Light-Emitting Devices Based on Quantum Dots with Tailored Nanostructures Nat Photon. 2015, 9, 259–266. 67. Oh, N.; Nam, S.; Zhai, Y.; Deshpande, K.; Trefonas, P.; Shim, M. DoubleHeterojunction Nanorods Nat. Commun. 2014, 5, 3642−3649. 68. Choi, H. S.; Liu, W.; Misra, P.; Tanaka, E.; Zimmer, J. P.; Ipe, B. I.; Bawendi, M. G.; Frangioni, J. V. Renal Clearance of Quantum Dots Nat. Biotechnol 2007, 25, 1165−1170. 69. Pons, T.; Pic, E.; Lequeux, N.; Cassette, E.; Bezdetnaya, L.; Guillemin, F.; Marchal, F.; Dubertret, B. Cadmium-Free CuInS2/ZnS Quantum Dots for Sentinel Lymph Node Imaging with Reduced Toxicity ACS Nano 2010, 4, 2531−2538. 70. Yu, J. H.; Kwon, S. H.; Petrášek, Z.; Park, O. K.; Jun, S. W.; Shin, K.; Choi, M.; Park, Y. I.; Park, K.; Na, H. B. High-Resolution Three- Photon Biomedical Imaging Using Doped ZnS Nanocrystals Nat. Mater. 2013, 12, 359−366. 71. Xu, G.; Zeng, S.; Zhang, B.; Swihart, M. T.; Yong, K.-T.; Prasad, P. N. New Generation Cadmium-Free Quantum Dots for Biophotonics and Nanomedicine Chem. Rev. 2016, 116, 12234−12327. 72. Ramasamy, P.; Ko, K. J.; Kang, J.-W.; Lee, J. S. Two Step “Seed-Mediated” Synthetic Approach to Colloidal Indium Phosphide Quantum Dots with High-Purity Photo-and Electroluminescence Chem. Mater. 2018, 30, 3643−3647.


Page 54 of 72

Page 55 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


73. Lim, J.; Park, M.; Bae, W. K.; Lee, D.; Lee, S.; Lee, C.; Char, K. Highly Efficient Cadmium-Free Quantum Dot Light-Emitting Diodes Enabled by the Direct Formation of Excitons within InP@ ZnSeS Quantum Dots ACS nano 2013, 7, 9019−9026. 74. Coughlan, C.; Ryan, K. M. Complete Study of the Composition and Shape Evolution in the Synthesis of Cu2ZnSnS4 (CZTS) Semiconductor Nanocrystals CrystEngComm 2015, 17, 6914−6922. 75. Ahmad, R.; Brandl, M.; Distaso, M.; Herre, P.; Spiecker, E.; Hock, R.; Peukert, W. A Comprehensive Study on the Mechanism Behind Formation and Depletion of Cu2ZnSnS4 (CZTS) Phases CrystEngComm 2015, 17, 6972−6984. 76. Chernomordik, B.; Béland, A.; Trejo, N.; Gunawan, A.; Deng, D.; Mkhoyan, K.; Aydil, E. Rapid Facile Synthesis of Cu2ZnSnS4 Nanocrystals J. Mater. Chem. A 2014, 2, 10389−10395. 77. Knowles, K. E.; Hartstein, K. H.; Kilburn, T. B.; Marchioro, A.; Nelson, H. D.; Whitham, P. J.; Gamelin, D. R. Luminescent Colloidal Semiconductor Nanocrystals Containing Copper: Synthesis, Photophysics, and Applications Chem. Rev 2016, 116, 10820−10851. 78. Goesmann, H.; Feldmann, C. Nanoparticulate Functional Materials Angew. Chem. Int. Ed. 2010, 49, 1362. 79. Kim, J. H.; Yang, H. High-Efficiency Cu–In–S Quantum-Dot-Light-Emitting Device Exceeding 7% Chem. Mater. 2016, 28, 6329−6335. 80. Wang, H.; Kim, D. H. Perovskite-Based Photodetectors: Materials and Devices Chem. Soc. Rev. 2017, 46, 5204−5236.



81. Konstantatos, G.; Sargent, E. H. Nanostructured Materials for Photon Detection Nat Nanotechnol, 2010, 5, 391–400. 82. Baeg, K. J.; Binda, M.; Natali, D.; Caironi, M.; Noh, Y. Y. Organic Light Detectors: Photodiodes and Phototransistors Adv. Mater. 2013, 25, 4267-4295. 83. Jansen‐van Vuuren, R. D.; Armin, A.; Pandey, A. K.; Burn, P. L.; Meredith, P. Organic Photodiodes: The Future of Full Color Detection and Image Sensing Adv. Mater. 2016, 28, 4766-4802. 84. Diedenhofen, S. L.; Kufer, D.; Lasanta, T.; Konstantatos, G. Integrated Colloidal Quantum Dot Photodetectors With Color-Tunable Plasmonic Nanofocusing Lenses Light Sci. Appl. 2015, 4, 234−240. 85. Konstantatos, G.; Clifford, J.; Levina, L.; Sargent, E. H. Sensitive Solution-Processed Visible-Wavelength Photodetectors Nat photonics 2007, 1, 531−534. 86. Böberl, M.; Kovalenko, M. V.; Gamerith, S.; List, E. J.; Heiss, W. Inkjet‐Printed Nanocrystal Photodetectors Operating up to 3 μm Wavelengths Adv. Mater. 2007, 19, 3574-3578. 87. Clifford, J. P.; Konstantatos, G.; Johnston, K. W.; Hoogland, S.; Levina, L.; Sargent, E. H. Fast, Sensitive and Spectrally Tuneable Colloidal-Quantum-Dot Photodetectors Nat Nanotechnol. 2009, 4, 40−44. 88. Yang, Z.; Wang, M.; Li, J.; Dou, J.; Qiu, H.; Shao, J. Spray-Coated CsPbBr3 Quantum Dot Films for Perovskite Photodiodes ACS Appl. Mater. Interfaces 2018, 10, 26387−26395.


Page 56 of 72

Page 57 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


89. Liu, S.; Li, M. Y.; Su, D.; Yu, M.; Kan, H.; Liu, H.; Wang, X.; Jiang, S. Broad-Band High-Sensitivity ZnO Colloidal Quantum Dots/Self-Assembled Au Nanoantennas Heterostructures Photodetectors ACS Appl. Mater. Interfaces 2018, 10, 32516−32525. 90. Ren, Z.; Sun, J.; Li, H.; Mao, P.; Wei, Y.; Zhong, X.; Hu, J.; Yang, S.; Wang, J. Bilayer PbS Quantum Dots for High‐Performance Photodetectors Adv. Mater. 2017, 29, 1702055. 91. Kan, H.; Zheng, W.; Lin, R.; Li, M.; Fu, C.; Sun, H.; Dong, M.; Xu, C.; Luo, J.; Fu, Y. R.; Huang, F. Ultra-Fast Photovoltaic-Type Deep-Ultraviolet Photodetector using Hybrid Zero-/Two-dimensional Heterojunctions ACS Appl. Mater. Interfaces 2019, 11, 8412–8418. 92. Zheng, W.; Huang, F.; Zheng, R.;

Wu, H. Low‐Dimensional Structure

Vacuum‐Ultraviolet‐Sensitive (λ< 200 nm) Photodetector with Fast‐Response Speed Based on High‐Quality AlN Micro/Nanowire Adv. Mater. 2015, 27, 3921-3927. 93. Zheng, W.; Lin, R.; Ran, J.; Zhang, Z.; Ji, X.; Huang, F. Vacuum-Ultraviolet Photovoltaic Detector ACS nano 2018, 12, 425–431. 94. Miao, J.; Zhang, F. Recent Progress on Highly Sensitive Perovskite Photodetectors J. Mater. Chem. C 2019, 7, 1741−1791. 95. Jeon, N. J.; Na, H.; Jung, E. H.; Yang, T. Y.; Lee, Y. G.; Kim, G.; Shin, H. W.; Seok, S. I.; Lee, J.; Seo, J. A Fluorene-Terminated Hole-Transporting Material for Highly Efficient and Stable Perovskite Solar Cells Nat. Energy, 2018, 3, 1093–1100. 96. Jiang, Q.; Chu, Z.; Wang, P.; Yang, X.; Liu, H.; Wang, Y.; Yin, Z.; Wu, J.; Zhang, X.; You, J. Planar‐Structure Perovskite Solar Cells with Efficiency Beyond 21% Adv. Mater. 2017, 29, 1703852.



97. An, Q.: Zhang, F.: Gao, W.; Sun, Q.: Zhang, M.; Yang, C.; Zhang, J. High-Efficiency and Air Stable Fullerene-Free Ternary Organic Solar Cells Nano Energy, 2018, 45, 177–183. 98. Zhang, M.: Zhang, F.; An, Q.; Sun, Q.; Wang, W.; Ma, X.; Zhang, J.; Tang, W. Nematic Liquid Crystal Materials as a Morphology Regulator For ternary small molecule solar cells with power conversion efficiency exceeding 10% J. Mater. Chem. A 2017, 5, 3589–3598. 99. Miao, J.; Zhang, F.; Lin, Y.; Wang, W.; Gao, M.; Li, L.; Zhang, J.; Zhan, X. Highly Sensitive Organic Photodetectors with Tunable Spectral Response under Bi‐Directional Bias Adv. Opt. Mater. 2016, 4, 1711-1717. 100. Song, J.; Cui, Q.; Li, J.; Xu, J.; Wang, Y.; Xu, L.; Xue, J.; Dong, Y.; Tian, T.; Sun, H.; Zeng, H. Ultralarge All‐Inorganic Perovskite Bulk Single Crystal for High‐Performance Visible–Infrared Dual‐Modal Photodetectors Adv. Opt. Mater. 2017, 5, 1700157. 101. Wang, Y.; Li, X.; Song, J.; Xiao, L.; Zeng, H.; Sun, H. All‐Inorganic Colloidal Perovskite Quantum dots: A New Class of Lasing Materials With Favorable Characteristics Adv.Mater. 2015, 27, 7101-7108. 102. Zhu, H.; Fu, Y.; Meng, F.; Wu, X.; Gong, Z.; Ding, Q.; Gustafsson, M.V.; Trinh, M. T.; Jin, S.; Zhu, X.Y. Lead Halide Perovskite Nanowire Lasers With Low Lasing Thresholds and High Quality Factors Nat. Mater. 2015, 14, 636−642. 103. Huang, C. Y.; Zou, C.; Mao, C.; Corp, K. L.; Yao, Y. C.; Lee, Y. J.; Schlenker, C.W.; Jen, A. K.; Lin, L. Y. CsPbBr3 Perovskite Quantum Dot Vertical Cavity Lasers With Low Threshold and High Stability ACS Photonics, 2017, 4, 2281−2289.


Page 58 of 72

Page 59 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


104. Chen, L. J.; Dai, J. H.; Lin, J. D.; Mo, T. S.; Lin, H. P.; Yeh, H. C.; Chuang, Y. C.; Jiang, S. A.; Lee, C. R. Wavelength-Tunable and Highly Stable Perovskite-QuantumDot-Doped Lasers with Liquid Crystal Lasing Cavities ACS Appl. Mater. Interfaces 2018, 10, 33307−33315. 105. Jamieson, T.; Bakhshi, R.; Petrova, D.; Pocock, R.; Imani, M.; Seifalian, A. M. Biological Applications of Quantum Dots Bio Mater. 2007, 28, 4717−4732. 106. Rosenthal, S. J.; Chang, J. C.; Kovtun, O.; McBride, J. R.; Tomlinson, I. D. Biocompatible Quantum Dots for Biological Applications Chem. Biol. 2011, 18, 10−24. 107. Ma, F.; Li, C. C.; Zhang, C. Y. Development of Quantum Dot-Based Biosensors: Principles and Applications J. Mater. Chem. A 2018, 6, 6173−6190. 108. Yu, M.; Zhao, K.; Zhu, X.; Tang, S.; Nie, Z.; Huang, Y.; Zhao, P.; Yao, S. Development of Near-Infrared Ratiometric Fluorescent Probe Based on Cationic Conjugated Polymer and CdTe/CdS QDs for Label-Free Determination of Glucose in Human Body Fluids Biosens Bioelectron. 2017, 95, 41−47. 109. Smith, A. M.; Mancini, M. C.; Nie, S. Bioimaging: Second Window for In Vivo Imaging Nat. Nanotechnol. 2009, 4, 710−711. 110. Fernández-Suárez, M.; Ting, A. Y. Fluorescent Probes for Super-Resolution Imaging in Living Cells Nat Rev Mol Cell Biol. 2008, 9, 929−943. 111. Monici, M. Cell and Tissue Autofluorescence Research and Diagnostic Applications Biotechnol Annu Rev. 2005, 11, 227−256. 112. Croce, A.; Bottiroli, G. Autofluorescence Spectroscopy and Imaging: A Tool For Biomedical Research and Diagnosis Eur J Histochem: EJH 2014, 58, 320−337.



113. Hong, G.; Antaris, A. L.; Dai, H. Near-Infrared Fluorophores for Biomedical Imaging Nat. Biomed. Eng. 2017, 1, 0010−0031. 114. Li, C.; Wang, Q. Challenge and Opportunities for Intravital Near-Infrared Fluorescence Imaging Technology in the Second Transparency Window ACS Nano 2018, 12, 9654−9659. 115. Kobayashi, H.; Ogawa, M.; Alford, R.; Choyke, P. L.; Urano, Y. New Strategies for Fluorescent Probe Design in Medical Diagnostic Imaging Chem Rev. 2009, 110, 2620−2640. 116. Yarema, M.; Pichler, S.; Sytnyk, M.; Seyrkammer, R.; Lechner, R. T.; Fritz-Popovski, G.; Jarzab, D.; Szendrei, K.; Resel, R.; Korovyanko, O. Infrared Emitting and Photoconducting Colloidal Silver Chalcogenide Nanocrystal Quantum Dots from a Silylamide-Promoted Synthesis ACS Nano 2011, 5, 3758−3765. 117. Kirchner, C.; Liedl, T.; Kudera, S.; Pellegrino, T.; Muñoz Javier, A.; Gaub, H. E.; Stölzle, S.; Fertig, N.; Parak, W. J. Cytotoxicity of Colloidal CdSe and CdSe/ZnS Nanoparticles Nano Lett. 2005, 5, 331−338. 118. Derfus, A. M.; Chan, W. C.; Bhatia, S. N. Probing the Cytotoxicity of Semiconductor Quantum Dots Nano Lett. 2004, 4, 11−18. 119. Zhang, W.; Lou, Q.; Ji, W.; Zhao, J.; Zhong, X. Color-Tunable Highly Bright Photoluminescence of Cadmium-Free Cu-doped Zn–In–S Nanocrystals and Electroluminescence Chem Mater. 2013, 26, 1204−1212. 120. Lv, G.; Guo, W.; Zhang, W.; Zhang, T.; Li, S.; Chen, S.; Eltahan, A. S.; Wang, D.; Wang, Y.; Zhang, J. Near-Infrared Emission CuInS/ZnS Quantum Dots: All-in-one


Page 60 of 72

Page 61 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Theranostic Nanomedicines with Intrinsic Fluorescence/Photoacoustic Imaging for Tumor Phototherapy ACS nano 2016, 10, 9637−9645. 121. Aharoni, A.; Mokari, T.; Popov, I.; Banin, U. Synthesis of InAs/CdSe/ZnSe core/shell1/shell2 structures with bright and stable near-infrared fluorescence J Am Chem Soc. 2006, 128, 257−264. 122. Gao, J.; Chen, K.; Xie, R.; Xie, J.; Lee, S.; Cheng, Z.; Peng, X.; Chen, X. Ultrasmall Near‐Infrared Non‐Cadmium Quantum Dots for In Vivo Tumor Imaging Small 2010, 6, 256-261. 123. Li, C. C.; Hu, J.; Lu, M.; Zhang, C. Y. Quantum Dot-Based Electrochemical Biosensor for Stripping Voltammetric Detection of Telomerase at the Single-Cell Level Biosens. Bioelectron. 2018, 122, 51−57. 124. Owen, J.; Brus, L, Chemical Synthesis and Luminescence Applications of Colloidal Semiconductor Quantum Dots J. Am. Chem. Soc. 2017, 139, 10939−10943. 125. Surrente, A.; Carron, R.; Gallo, P.; Rudra, A.; Dwir, B.; Kapon, E. Self-Formation of Hexagonal Nanotemplates for Growth of Pyramidal Quantum Dots by Metalorganic Vapor Phase Epitaxy on Patterned Substrates Nano Res. 2016, 3279−3290. 126. Paul, M.; Kettler, J.; Zeuner, K.; Clausen, C.; Jetter, M.; Michler, P. Metal-Organic Vapor-Phase Epitaxy-Grown Ultra-Low Density InGaAs/GaAs Quantum Dots Exhibiting Cascaded Single-Photon Emission at 1.3 μm Appl. Phys. Lett. 2015, 106, 122105−122108. 127. Prasad, K.; Jha, A. K. Biosynthesis of CdS Nanoparticles: An Improved Green and Rapid Procedure J. Colloid Interface Sci. 2010, 342, 68−72.



128. Sweeney, R. Y.; Mao, C.; Gao, X.; Burt, J. L.; Belcher, A. M.; Georgiou, G.; Iverson, B. L. Bacterial Biosynthesis of Cadmium Sulfide Nanocrystals Chem. Biol. 2004, 11, 1553−1559. 129. Ouyang, J.; Zaman, M. B.; Yan, F. J.; Johnston, D.; Li, G.; Wu, X.; Leek, D.; Ratcliffe, C. I.; Ripmeester, J. A.; Yu, K. Multiple Families of Magic-Sized CdSe Nanocrystals with Strong Bandgap Photoluminescence via Noninjection One-Pot Syntheses J. Phys. Chem. C. 2008, 112, 13805−13811. 130. Mekis, I.; Talapin, D. V.; Kornowski, A.; Haase, M.; Weller, H. One-Pot Synthesis of Highly Luminescent CdSe/CdS Core−Shell Nanocrystals via Organometallic and “Greener” Chemical Approaches J. Phys. Chem. B 2003, 107, 7454−7462. 131. Deng, Z.; Cao, L.; Tang, F.; Zou, B. A New Route to Zinc-Blende CdSe Nanocrystals: Mechanism and Synthesis J. Phys. Chem. B 2005, 109, 16671−16675. 132. Wang, A.; Yan, X.; Zhang, M.; Sun, S.; Yang, M.; Shen, W.; Pan, X.; Wang, P.; Deng, Z. Controlled Synthesis of Lead-Free and Stable Perovskite Derivative Cs2SnI6 Nanocrystals via a Facile Hot-Injection process Chem. Mater. 2016, 28, 8132−8140. 133. Fu, T.; Qin, H.-Y.; Hu, H.-J.; Hong, Z.; He, S. Aqueous Synthesis and FluorescenceImaging Application of CdTe/ZnSe Core/Shell Quantum Dots with High Stability and Low Cytotoxicity J. Nanosci. Nanotechnol. 2010, 10, 1741−1746. 134. Tan, J.; Liang, Y.; Wang, J.; Chen, J.; Sun, B.; Shao, L. Facile Synthesis of CdTeBased Quantum Dots Promoted by Mercaptosuccinic Acid and Hydrazine New J. Chem. 2015, 39, 4488−4493.


Page 62 of 72

Page 63 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


135. Vikram, A.; Kumar, V.; Ramesh, U.; Balakrishnan, K.; Oh, N.; Deshpande, K.; Ewers, T.; Trefonas, P.; Shim, M.; Kenis, P. J. A Millifluidic Reactor System for Multistep Continuous Synthesis of InP/ZnSeS Nanoparticles ChemNanoMat. 2018, 4, 943-953. 136. Nightingale, A. M.; de Mello, J. C. Microscale Synthesis of Quantum Dots J. Mater. Chem. 2010, 20, 8454−8463. 137. Kwon, B. H.; Lee, K. G.; Park, T. J.; Kim, H.; Lee, T. J.; Lee, S. J.; Jeon, D. Y. Continuous In Situ Synthesis of ZnSe/ZnS Core/Shell Quantum Dots in a Microfluidic Reaction System and its Application for Light‐Emitting Diodes Small 2012, 8, 3257. 138. Edel, J. B.; Fortt, R. Microfluidic Routes to the Controlled Production of Nanoparticles Chem. Commun, 2002, 1136−1137. 139. Sebastian Cabeza, V.; Kuhn, S.; Kulkarni, A. A.; Jensen, K. F. Size-Controlled Flow Synthesis of Gold Nanoparticles Using a Segmented Flow Microfluidic Platform Langmuir 2012, 28, 7007−7013. 140. Duraiswamy, S.; Khan, S. A. Droplet‐Based Microfluidic Synthesis of Anisotropic Metal Nanocrystals Small 2009, 5, 2828−2834. 141. Kim, Y. H.; Zhang, L.; Yu, T.; Jin, M.; Qin, D.; Xia, Y. Droplet‐Based Microreactors for Continuous Production of Palladium Nanocrystals with Controlled Sizes and Shapes Small 2013, 9, 3462−3467. 142. Lignos, I.; Maceiczyk, R.; deMello, A. J. Microfluidic Technology: Uncovering the Mechanisms of Nanocrystal Nucleation and Growth Acc. Chem. Res. 2017, 50, 1248−1257. 143. Wan, Z.; Luan, W.; Tu, S. T. Size Controlled Synthesis of Blue Emitting Core/Shell Nanocrystals via Microreaction J. Phys. Chem. C 2010, 115, 1569−1575.



144. Epps, R. W.; Felton, K. C., Coley.; C. W.; Abolhasani, M. Automated Microfluidic Platform for Systematic Studies of Colloidal Perovskite Nanocrystals: Towards Continuous Nano-Manufacturing Lab Chip 2017, 17, 4040−4047. 145. Tice, J. D.; Song, H.; Lyon, A. D.; Ismagilov, R. F. Formation of Droplets and Mixing in Multiphase Microfluidics at Low Values of the Reynolds and the Capillary Numbers Langmuir 2003, 19, 9127−9133. 146. Yang, H.; Luan, W.; Wan, Z.; Tu, S. T.; Yuan, W.-K.; Wang, Z. M. Continuous Synthesis of Full-Color Emitting Core/Shell Quantum Dots via Microreaction Cryst. Growth Des. 2009, 9, 4807−4813. 147. L. Guo, S. Z., L. Cheng, Y. Song. Comparative Analysis of Mixing Performance and Pressure Loss of Three Types of Passive Micromixers. In Electronic Measurement & Instruments, ICEMI'09. 9th International Conference on 2009 IEEE 2009, 1−538. 148. Toyota, A.; Nakamura, H.; Ozono, H.; Yamashita, K.; Uehara, M.; Maeda, H. Combinatorial Synthesis of CdSe Nanoparticles Using Microreactors J. Phys. Chem. C 2010, 114, 7527−7534. 149. Krishnadasan, S.; Tovilla, J.; Vilar, R. On-Line Analysis of CdSe Nanoparticle Formation in a Continuous Flow Chip-Based Microreactor J. Mater. Chem. 2004, 14, 2655−2660. 150. Günther, A.; Jhunjhunwala, M.; Thalmann, M.; Schmidt, M. A.; Jensen, K. F. Micromixing of Miscible Liquids in Segmented Gas−Liquid Flow Langmuir 2005, 21, 1547−1555.


Page 64 of 72

Page 65 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


151. Nightingale, A. M.; Bannock, J. H.; Krishnadasan, S. H.; O'Mahony, F. T.; Haque, S. A.; Sloan, J.; Drury, C.; McIntyre, R. Large-Scale Synthesis of Nanocrystals in a Multichannel Droplet Reactor J. Mater. Chem. A 2013, 1, 4067−4076. 152. Lu, L. H.; Ryu, K. S.; Liu, C. A Magnetic Microstirrer and Array for Microfluidic Mixing J. MEMS. 2002, 11, 462−469. 153. Jo, B. H.; Van Lerberghe, L. M.; Motsegood, K. M.; Beebe, D. J. Three-Dimensional Micro-Channel Fabrication in Polydimethylsiloxane (PDMS) Elastomer J. MEMS. 2000, 9, 76−81. 154. Liu, R. H.; Yang, J.; Pindera, M. Z.; Athavale, M.; Grodzinski, P. Bubble-Induced Acoustic Micromixing Lab hip 2002, 2, 151−157. 155. Yang, Z.; Matsumoto, S.; Goto, H.; Matsumoto, M.; Maeda, R. Ultrasonic Micromixer for Microfluidic Systems Sens. Actuators. A 2001, 93, 266−272. 156. Wu, H.-Y.; Liu, C. H. A Novel Electrokinetic Micromixer Sens. Actuators. A 2005, 118, 107−115. 157. Losey, M. W.; Schmidt, M. A.; Jensen, K. F. Microfabricated Multiphase Packed-Bed Reactors: Characterization of Mass Transfer and Reactions Ind. Eng. Chem. Res. 2001, 40, 2555−2562. 158. Bessoth, F. G.; Manz, A. Microstructure for Efficient Continuous Flow Mixing Anal Commun. 1999, 36, 213−215. 159. Liu, R. H.; Stremler, M. A.; Sharp, K. V.; Olsen, M. G.; Santiago, J. G.; Adrian, R. J.; Aref, H.; Beebe, D. J. Passive Mixing in a Three-Dimensional Serpentine Microchannel J. MEMS. 2000, 9, 190−197.



160. Bessoth, F. G.; deMello, A. J.; Manz, A. 10th Int. Conf. on Solid-State Sensors and Actuators, Sendai, Japan 1999, 200−203. 161. Maceiczyk, R. M.; Lignos, I. G. Online Detection and Automation Methods in Microfluidic Nanomaterial Synthesis Curr. Opin. Chem. Eng. 2015, 8, 29−35. 162. Chan, E. M.; Mathies, R. A.; Alivisatos, A. P. Size-Controlled Growth of CdSe Nanocrystals in Microfluidic Reactors Nano Lett. 2003, 3, 199−201. 163. Chan, E. M.; Alivisatos, A. P.; Mathies, R. A. High-temperature Microfluidic Synthesis of CdSe Nanocrystals in Nanoliter Droplets J. Am. Chem. Soc. 2005, 127, 13854−13861. 164. Nakamura, H.; Yamaguchi, Y.; Miyazaki, M.; Maeda, H.; Uehara, M.; Mulvaney, P. Preparation of CdSe Nanocrystals in a Micro-Flow-Reactor Chem. Commun. 2002, 0, 2844−2845. 165. Yen, B. K.; Stott, N. E.; Jensen, K. F.; Bawendi, M. G. A Continuous‐Flow Microcapillary Reactor for the Preparation of a Size Series of CdSe Nanocrystals Adv.Mater. 2003, 15, 1858−1862. 166. Wang, H.; Li, X.; Uehara, M.; Yamaguchi, Y.; Nakamura, H.; Miyazaki, M.; Shimizu, H.; Maeda, H. Continuous Synthesis of CdSe–ZnS Composite Nanoparticles in a Microfluidic Reactor Chem. Commun. 2004, 0, 48−49. 167. Nakamura, H.; Tashiro, A.; Yamaguchi, Y.; Miyazaki, M.; Watari, T.; Shimizu, H.; Maeda, H. Application of a Microfluidic Reaction System for CdSe Nanocrystal Preparation: Their Growth Kinetics and Photoluminescence Analysis Lab Chip 2004, 4, 237−240.


Page 66 of 72

Page 67 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


168. Wang, H.; Nakamura, H.; Uehara, M.; Yamaguchi, Y.; Miyazaki, M.; Maeda, H. Highly Luminescent CdSe/ZnS Nanocrystals Synthesized Using a Single‐Molecular ZnS Source in a Microfluidic Reactor Adv. Funct. Mater. 2005, 15, 603−608. 169. Shestopalov, I.; Tice, J. D.; Ismagilov, R. F. Multi-Step Synthesis of Nanoparticles Performed on Millisecond Time Scale in a Microfluidic Droplet-Based System Lab Chip 2004, 4, 316−321. 170. Yen, B. K.; Günther, A.; Schmidt, M. A.; Jensen, K. F.; Bawendi, M. G. A Microfabricated Gas–Liquid Segmented Flow Reactor for High‐Temperature Synthesis: The Case of CdSe Quantum Dots Angew. Chem., Int. Ed. 2005, 44, 5447−5451. 171. Marre, S.; Park, J.; Rempel, J.; Guan, J.; Bawendi, M. G.; Jensen, K. F. Supercritical Continuous‐Microflow Synthesis of Narrow Size Distribution Quantum Dots Adv.Mater. 2008, 20, 4830−4834. 172. Naughton, M. S.; Kumar, V.; Bonita, Y.; Deshpande, K.; Kenis, P. J. High Temperature Continuous Flow Synthesis of CdSe/CdS/ZnS, CdS/ZnS, and CdSeS/ZnS Nanocrystals Nanoscale 2015, 7, 15895−15903. 173. Pan, J.; El-Ballouli, A. A. O.; Rollny, L.; Voznyy, O.; Burlakov, V. M.; Goriely, A.; Sargent, E. H.; Bakr, O. M. Automated Synthesis of Photovoltaic-Quality Colloidal Quantum Dots Using Separate Nucleation and Growth Stages ACS nano, 2013, 7, 10158−10166. 174. Lignos, I.; Protesescu, L.; Stavrakis, S.; Piveteau, L.; Speirs, M. J.; Loi, M. A.; Kovalenko, M. V.; deMello, A. J. Facile Droplet-Based Microfluidic Synthesis of



Monodisperse IV–VI Semiconductor Nanocrystals with Coupled In-Line NIR Fluorescence Detection Chem. Mater. 2014, 26, 2975−2982. 175. Brunetti, V.; Chibli, H.; Fiammengo, R.; Galeone, A.; Malvindi, M. A.; Vecchio, G.; Cingolani, R.; Nadeau, J. L.; Pompa, P. P. InP/ZnS as a Safer Alternative to CdSe/ZnS Core/Shell Quantum Dots: In Vitro and In Vivo Toxicity Assessment Nanoscale 2013, 5, 307−317. 176. Chibli, H.; Carlini, L.; Park, S.; Dimitrijevic, N. M.; Nadeau, J. L. Cytotoxicity of InP/ZnS Quantum Dots Related to Reactive Oxygen Species Generation Nanoscale 2011, 3, 2552−2559. 177. Nightingale, A. M.; de Mello, J. C. Controlled Synthesis of III–V Quantum Dots in Microfluidic Reactors ChemPhysChem 2009, 10, 2612−2614. 178. Jo, J. H.; Kim, J. H.; Lee, K. H.; Han, C. Y.; Jang, E. P.; Do, Y. R.; Yang, H. HighEfficiency Red Electroluminescent Device Based on Multishelled InP Quantum Dots Opt. Lett. 2016, 41, 3984−3987. 179. Baek, J.; Allen, P. M.; Bawendi, M. G.; Jensen, K. F. Investigation of Indium Phosphide Nanocrystal Synthesis Using a High‐Temperature and High‐Pressure Continuous Flow Microreactor Angew. Chem. Int. Ed. 2011, 50, 627−630. 180. Kim, K.; Jeong, S.; Woo, J. Y.; Han, C. S. Successive and Large-Scale Synthesis of InP/ZnS Quantum Dots in a Hybrid Reactor and Their Application to White LEDs Nanotech. 2012, 23, 065602. 181. Ippen, C.; Schneider, B.; Pries, C.; Kröpke, S.; Greco, T.; Holländer, A. Large-Scale Synthesis of High Quality InP Quantum Dots in a Continuous Flow-Reactor Under Supercritical Conditions Nanotech. 2015, 26, 085604−085610.


Page 68 of 72

Page 69 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


182. Baek, J.; Shen, Y.; Lignos, I.; Bawendi, M. G.; Jensen, K. F. Multistage Microfluidic Platform for the Continuous Synthesis of III–V Core/Shell Quantum Dots Angew.Chem. 2018, 130, 11081−11084. 183. Yashina, A.; Lignos, I.; Stavrakis, S.; Choo, J. Scalable Production of CuInS2/ZnS Quantum Dots in a Two-Step Droplet-Based Microfluidic Platform J. Mater. Chem. C 2016, 4, 6401−6408. 184. Aldakov, D.; Lefrançois, A.; Reiss, P. Ternary and Quaternary Metal Chalcogenide Nanocrystals: Synthesis, Properties and Applications J. Mater. Chem. C 2013, 1, 3756−3776. 185. Deng, D.; Chen, Y.; Cao, J.; Tian, J.; Qian, Z.; Achilefu, S.; Gu, Y. High-Quality CuInS2/ZnS Quantum Dots for In Vitro and In Vivo Bioimaging Chem. Mater. 2012, 24, 3029−3037. 186. Song, W.S.; Yang, H. Efficient White-Light-Emitting Diodes Fabricated from Highly Fluorescent Copper Indium Sulfide Core/Shell Quantum Dots Chem. Mater. 2012, 24, 1961−1967. 187. Park, S. H.; Hong, A.; Kim, J. H.; Yang, H.; Lee, K.; Jang, H. S. Highly Bright YellowGreen-Emitting CuInS2 Colloidal Quantum Dots with Core/Shell/Shell Architecture for White Light-Emitting Diodes ACS Appl. Mater. Interfaces 2015, 7, 6764−6771. 188. Lee, J.; Han, C. S. Large-Scale Synthesis of Highly Emissive and Photostable CuInS 2/ZnS

Nanocrystals Through Hybrid Flow Reactor Nanoscale Res. Lett. 2014, 9,

78−85.



189. Li, S.; Chen, Y.; Huang, L.; Pan, D. Simple Continuous-Flow Synthesis of Cu–In– Zn–S/ZnS and Ag–In–Zn–S/ZnS Core/Shell Quantum Dots Nanotech. 2013, 24, 395705−395710. 190. Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V. Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X= Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut Nano Lett. 2015, 15, 3692−3696. 191. Lignos, I.; Stavrakis, S.; Nedelcu, G.; Protesescu, L.; deMello, A. J.; Kovalenko, M. V. Synthesis of Cesium Lead Halide Perovskite Nanocrystals in a Droplet-Based Microfluidic Platform: Fast Parametric Space Mapping Nano Lett. 2016, 16, 1869−1877. 192. Maceiczyk, R. M.; Dümbgen, K.; Lignos, I.; Protesescu, L.; Kovalenko, M. V.; deMello, A. J. Microfluidic Reactors Provide Preparative and Mechanistic Insights into the Synthesis of Formamidinium Lead Halide Perovskite Nanocrystals Chem. Mater 2017, 29, 8433−8439. 193. Lignos, I.; Protesescu, L.; Emiroglu, D. B. r.; Maceiczyk, R.; Schneider, S.; Kovalenko, M. V.; deMello, A. J. Unveiling the Shape Evolution and Halide-IonSegregation in Blue-Emitting Formamidinium Lead Halide Perovskite Nanocrystals Using an Automated Microfluidic Platform Nano Lett. 2018, 18, 1246−1252. 194. Lignos, I.; Morad, V.; Shynkarenko, Y.; Bernasconi, C.; Maceiczyk, R. M.; Protesescu, L.; Bertolotti, F.; Kumar, S.; Ochsenbein, S. T.; Masciocchi, N. Exploration of Near Infrared-Emissive Colloidal Multinary Lead Halide Perovskite Nanocrystals using an Automated Microfluidic Platform ACS Nano 2018, 12, 5504–5517.


Page 70 of 72

Page 71 of 72 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


195. Ma, K.; Du, X. Y.; Zhang, Y. W.; Chen, S. In Situ Fabrication of Halide Perovskite Nanocrystals Embedded in Polymer Composites via Microfluidic Spinning Microreactors J. Mater. Chem. C 2017, 5, 9398−9404. 196. Song, Y. H.; Choi, S. H.; Park, W. K.; Yoo, J. S.; Kwon, S. B.; Kang, B. K.; Park, S. R.; Seo, Y. S.; Yang, W. S.; Yoon, D. H. Innovatively Continuous Mass Production Couette-Taylor Flow: Pure Inorganic Green-Emitting Cs4PbBr6 Perovskite Microcrystal for Display Technology Sci. Rep. 2018, 8, 2009−2014. 197. Bao, Z.; Wang, H. C.; Jiang, Z. F.; Chung, R. J.; Liu, R. S. Continuous Synthesis of Highly Stable Cs4PbBr6 Perovskite Microcrystals by a Microfluidic System and Their Application in White-Light-Emitting Diodes Inorg. Chem. 2018, 57, 13071−13074.



TOC


Page 72 of 72

Microfluidic Synthesis of Semiconducting Colloidal Quantum Dots and

Recommend Documents