From Large Scale Synthesis to Lighting Device Applications of Ternary

Perspective Cite This: J. Phys. Chem. Lett. 2018, 9, 435−445

pubs.acs.org/JPCL

From Large-Scale Synthesis to Lighting Device Applications of Ternary I−III−VI Semiconductor Nanocrystals: Inspiring Greener Material Emitters Bingkun Chen,*,§ Narayan Pradhan,*,‡ and Haizheng Zhong*,† §

Beijing Engineering Research Centre of Mixed Reality and Advanced Display, School of Optics and Photonics, Beijing Institute of Technology, Beijing 100081, China † Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems, School of Materials Science & Engineering, Beijing Institute of Technology, Beijing 100081, China ‡ Department of Materials Science, Indian Association for the Cultivation of Science, Kolkata, India 700032 ABSTRACT: Quantum dots with fabulous size-dependent and color-tunable emissions remained as one of the most exciting inventories in nanomaterials for the last 3 decades. Even though a large number of such dot nanocrystals were developed, CdSe still remained as unbeatable and highly trusted lighting nanocrystals. Beyond these, the ternary I−III−VI family of nanocrystals emerged as the most widely accepted greener materials with efficient emissions tunable in visible as well as NIR spectral windows. These bring the high possibility of their implementation as lighting materials acceptable to the community and also to the environment. Keeping these in mind, in this Perspective, the latest developments of ternary I−III−VI nanocrystals from their large-scale synthesis to device applications are presented. Incorporating ZnS, tuning the composition, mixing with other nanocrystals, and doping with Mn ions, light-emitting devices of single color as well as for generating white light emissions are also discussed. In addition, the future prospects of these materials in lighting applications are also proposed.

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the ternary family of NCs here shows the widest window emission with their size and composition variations. Among the special features, these materials possess a longer excited-state lifetime, spectral broadening of a large full width at halfmaximum (fwhm), wide Stokes shifts, high quantum efficiency, easy and cost-effective synthesis, and certainly have all greener elements. The composition variations bring complicated photophyics, which still need further investigations.37−39 Although recent work indicates that the large broadening of the CuInS2 NC ensemble spectra is not intrinsic but a result of dot-to-dot variations in the emission energy, there is still no practical way to achieve the narrow-band emissions.40 Figure 1b presents a comparison of spectral characteristics and different optical features of these materials. The features of broad emissions, easy scale-up synthesis, and low cost make them more suitable materials for achieving high-quality general lighting. A search of literature reports reveals that these ternary NCs were reported close to a decade ago,20−26,41−46 and these have also been tremendously studied and implemented in different potential applications.27−34 Among these, light to light energy,27,47−53 light to chemical energy, 54−57 light to electricity,44,58−63 and light to signal64−66 were extensively

ight-emitting semiconductor nanocrystals (NCs), widely known as quantum dots (QDs), have emerged as one of the leading dispersed lighting materials with efficient and tunable emissions for decades.1−5 Athough the first commercialized material CdSe NCs have a serious toxic Cd problem, they are still ruling as the work horse and most accessed material toward industrialization.6−11 Enormous efforts have been put forward to find alternative environment benign greener materials for technological applications, leading to use in day-to-day life. Over the course of time, InP and different Cd free doped NCs with high-bandgap host materials have also been developed,12−16 but still these are not able to run parallel to the full visible spectral window tunable CdSe NCs.17−19 In comparison, group I−III−VI ternary NCs are rare greener materials that have emerged to date that have an acceptable level of emission intensity, tunable in the entire visible and NIR window, and importantly are free from Cd-like toxic elements.20−34 These greener materials to date retain hope for today’s technological applications for their merits of low cost and easy processing; however, extensive focus is needed to improve the quality, surface modification, device fabrication, and prosessing techniques for commercialization. Even though recently developed perovskite NCs have unprecedented high quantum efficiency, they still remain elusive for daily life device applications because of the element Pb, whose toxicity is also a pronounced problem.35,36 Figure 1a shows different dispersed colloidal NCs developed to date and their tunable emission spectral windows. No doubt, © XXXX American Chemical Society

Received: November 15, 2017 Accepted: January 5, 2018 Published: January 5, 2018 435

DOI: 10.1021/acs.jpclett.7b03037 J. Phys. Chem. Lett. 2018, 9, 435−445

The Journal of Physical Chemistry Letters

Perspective

Figure 1. (a) Tunable spectral windows of different colloidal semiconductor NCs. (b) Approximate wavelength ranges and PL properties of different groups of semiconductors and perovskite NCs. Note: data ① from ref 17, data ② from ref 15, data ③ from ref 36, data ④ from refs 27, 59, 67, and 76.

be occupied in either Cu(I) and/or In(III) ions in the crystal lattice. Further, the alloyed structure is shown shelled to boost the emission intensity. The exact composition here would be CuI(1−x)MIII(1−y)ZnII(x+y)/2SVI2/ZnS, but for simplicity, the name was referred to as CZIS (Cu Zn In S and as per increasing group order I−II−III−V), where the elementals were arranged alphabetically. Figure 3a shows the combined PL spectra obtained from CuInS2 and CuInSe2 NCs tunable in the visible and NIR spectral window. This optical tuning with composition variations and Zn incorporation has been extensively reported.27,75,76 The synthesis has also been extended to the gram scale for commercializing the material. Figure 3b,c shows the representative reaction setup and the obtained products in a large-scale synthesis of CZIS NCs, respectively. The availability of tens of grams of high-quality materials bring versatility to their widespread applications, including lighting, luminescent solar concentrators, biolabeling, chemical sensors, etc.27 The broad emission covering most of the visible region and easy processing from solution enable these materials as white light emitters with better color quality, showing a bright future to compete with rare earth-based phosphors. Ga as the trivalent ions further tunes the emission toward the deeper blue region,77 while doping Mn enables the ability to emit white light as well as interesting magneto-optical properties.78−80 Figure 3d presents the CIE chromaticity coordinates for CuGaS2, CuInS2, and AgInS2 NCs with possible color windows.81−83 This provides guidelines for obtaining white light with proper a mixture for making white light-emitting devices.84 These also vary with respective selenide counters.85,86 The first and foremost requirement of these materials for device applications is their processeability retaining the original optical properties.87−89 For solvent evaporation-induced film deposition, dispersity of these NCs in different solvents with a variable boiling point and polarity is essentially required. Hence, the as-synthesized NCs demand surface modifications with appropriate ligands. The aqueous and nonaqueous transfer by such surface modifications, which are common for other conventional colloidal NCs, are also extended to these I−III− VI semiconductor NCs.88 However, most of such phase transfer strategies were aimed at bioapplications and might not be capable for scale-up fabrication as required for device fabrications. Aiming to extend the processability, recently, alcohol-soluble NCs in polar solvents (methanol, ethanol, DMF) were developed by modifying the surface with −OH group ending ligands.89−91 These alcohol-soluble dots not only provide green solvents for processing but also give a moderate

The features of broad emissions, easy scale-up synthesis, and low cost make them more suitable materials for achieving highquality general lighting. studied. However, despite all of these successes, these materials still need more focus for commercialization as efficient luminescent materials for general warm light room illumination.68−73 Keeping this in mind, herein, the current prospects of these materials as lighting source for device applications are the focus. In addition, the chemistry of synthesis for large-scale surface modifications and spectral evolutions for white light formation is also addressed. Further, future prospects of these nanostructures as lighting materials is also discussed. From literature reports, it is observed that different research groups refer to different chemical and composition variable identities of these materials. The ideal case for enhancing the optical emission is Zn incorporation in ternary I−III−V NCs followed by ZnS shell growth. For the case of CuInS2, these NCs are named as Cu−In−S/ZnS, Cu−In−Zn−S/ZnS, CuInS2/ZnS, etc., but the most appropriate structure is the alloyed Cu−In−Zn−S followed by the shell of ZnS.72,74 A representative model for the most likely structure is presented in Figure 2, where Zn was shown as alloy in CuInS2 and could

Figure 2. Schematic presentation of the composition and alloyed core CIZS/shelled ZnS nanostructures. In the ternary system, MI is for CuI and AgI, MII represents InIII and GaIII, and E stands for SVI and SeVI. 436



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Figure 3. (a) PL spectra of composition tunable and ZnS shelled CuInS2 and CuInSe2 NCs. The excited wavelength is 370 nm. (b,c) Digital images of the reaction flask and purified CIZS NCs in gram scale synthesis. (d) CIE chromaticity coordinates showing CuInS2, AgInS2, and CuGaS2 NCs.77,81−83

Figure 4. (a) Schematic presentation of different surface ligands for solubilizing NCs in organic, alcohol, and the aqueous phase. (b) Schematic presentation of an in situ ligand exchange process for alcohol-soluble NCs. This figure is adopted from ref 90.

for the NCs without a shell or thin-shell samples but is less pronounced for the samples with thick shells. This phenomenon can be explained by the introduction of surface traps during the ligand exchange process.90 To avoid the PL

rate of solvent evaporation compared to that in water or in organic solvents such as toluene or chloroform. Figure 4a shows a series of organic surface ligands for oil-, alcohol-, and water-solubilizing NCs. As the alcohol-soluble approach is newly developed, the process is elaborately discussed here as a representative one. The schematic presentation of step variation for such surface modification is shown in Figure 4b. Unlike the aqueous and nonaqueous phase transfer between two liquid phases, the modification of −OH group ending ligands employs transformation between a colloidal solution and solid aggregates. This phase transfer can be accomplished by either ex situ or in situ methods. In a typical ex situ experiment, the preformed colloidal NCs in the solid state (powder) is dispersed in DMF and heated at 120 °C in the presence of 6-mercaptohexanol (MCH) as a ligand. After ligand exchange, the mixture turns to transparent from turbid, indicating the surface modification of MCH molecules. The MCH-capped colloidal NCs can be precipitated from solution and dispersed in other polar solvents (even water). Depending on the composition and structure of the preformed NCs, the phase transfer into alcohol-soluble NCs may bring PL quenching effects. It is noted that PL quenching is significant

To avoid the PL quenching effects, the in situ phase transformation of CuInS2-based NCs may be demonstrated by combining the ligand exchange process with colloidal synthesis. quenching effects, the in situ phase transformation of CuInS2based NCs may be demonstrated by combining the ligand exchange process with colloidal synthesis. Typically, the colloidal synthesis of CZIS NCs is similar to that developed for oil-soluble materials. After the colloidal synthesis, a fixed amount of MCH was injected into the reaction mixture at 180 °C and kept for 15 min. The MCH-capped CZIS NCs precipitated from solution and could be well-dispersed into 437



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Table 1. Parameters of Phosphor Converted White LEDs by Using I−III−VI NCsa

a

NCs

CRI

CCT (K)

LER (lm/Wopt)

ZnCuInS2/ZnS CuInS2/ZnS Ba2SiO4(green) YAG:Ce-CIS/ZnS CuInS2 NCs CuInS2 CuInS2 + rare earth phosphor Ba2SiO4:Eu2−CIS/ZnS CuInS2 + rare earth phosphor CIS/ZnS/ZnS (Mn,Cu):Zn−In− S/ZnS Cu: ZnInS/ZnS Mn-doped Zn−Cu−In−S NCs CuInS2 NCs + Al(OH)3

83.8 90 84 75 95 92 90 93 73 95 96 90 94.3

3237.4 5784 2784 4447−5380 4600−5600 11304−3402 6552 5749 6140 5092 5760 5680 5301

4.15 23.8 30.6 63.4 70 60 lm/W 36.7 80.3 73.2 78 23.5

current (mA)

20 20 20 40 20

LED chips (nm)

ref

430 440 450 450 450 450 455 450 450 450 450 460 405

99 100 101 102 82 67 103 104 105 106 106 107 108

20 20 20 20 20 20 20 30 mA mA mA mA mA

CRI = color rendering index, CCT = correlated color temperature, LER = luminous efficiencies.

Table 2. Performance of I−III−VI NC-Based EL Devices materials

wavelength (nm)

CuInS2/ZnS CuInS2/ZnS CuInS2−ZnS

500−800 560 560, 594, 632

Cu-doped Zn−In−Se

585−673

Ag−In−Zn−S/ZnS

525−570

CuInS2/ZnS ZnCuInS/ZnS Cu−In−Zn−S/ZnS Cu−In−Zn−S/ZnS

577−602 white light (400−800) 550 600−650

Cu−Ga−S/ZnS

470−580

devices structure ITO/PEDOT:PSS/QDs/ZnO/Ga/Al ITO/ZnO/QDs/CBP/TCTA/MoO3/Al ITO/PEDOT:PSS/PloyTPD/QDs/ Alq3/Ca/Al ITO/PEDOT:PSS/PloyTPD/QDs/ ZnO/Al ITO/PEDOT:PSS/PVK/AIZS/ZnS QDs/ZnO NP/Al ITO/PEDOT:PSS/TFB/QDs/ZnO/Al ITO/PEDOT:PSS/PloyTPD/QDs/Al ITO/PEDOT:PSS/TFB/QDs/ZnO/Al ITO/PEDOT:PSS/PloyTPD/QDs/ ZnO/Al ITO/PEDOT:PSS/PVK/QDs/ZnO/Al

luminance (cd m−2)

current efficiency (cd A−1)

2100 8375 1200−1600

0.92 9.43 0.58−0.82

320

0.97

698

0.36

8464 450 1500

1007

18.2

EL efficiency (EQE) (%)

ref

3.22

76 89 122 123

0.49

124

7.3 0.033 0.37

125 126 127 128

1.9

129

0.13

3.6

to 95.82 However, the on-chip devices suffer from serious degradation issues due to the high temperature under working conditions. This challenge also hindered the use of CdSe NCbased on-chip devices in LCD display backlights.94,109 A remote-type configuration separates the color-converting materials, with blue emissive chips at an appropriate distance, providing a possible way to solve the dissipation problem and bring a relative larger lighting area.69,70 In this configuration, the key component is the color-converting plates. The inherently small size and solution processability of colloidal NCs match well the requirements. The initial prototype devices already show the advantages to realize general illumination.110,111 Incorporating colloidal NCs into transparent matrixes is a crucial step to achieve the color conversion plates. The spatial distribution and loading content of NCs in the matrixes are important parameters in determining the performance for lighting. Currently, the lack of appropriate strategies and suitable matrixes is still the most concerning challenge.8,112 Electroluminescence Devices. The EL devices that are constructed using multilayer thin films have been well demonstrated in organic light-emitting diodes (OLEDs), which are now on the way to commercialization in the field of panel display.113 There has been a long history of 23 years since the first report of CdSe NC-based EL devices.114−118 After years of efforts on material optimizations, the device performance of CdSe-based devices is now comparable to or even better than that of organic molecular-based counterparts,7

nonpolar solvents. The advances of these alcohol-soluble NCs significantly benefit the device applications, as discussed in the following device part.89−91 Phosphor-Converted White Light-Emitting Diodes (pc-WLEDs). Pc-WLEDs that combined blue-emitting chips with downconverting phosphors are now commercialized products to replace incandescent lamps and/or compact fluorescent lamps. Concerning the demand of low-cost, high-efficiency, and highcolor-rendering WLEDs for general large-area illumination, rare earth phosphors are now facing challenges for their insufficient supply and limited spectral tunability.92,93 Although the integration of well-developed CdSe94,95 and InP96−98 based NCs with blue-emitting chips had been successfully demonstrated, the general illumination technology is not able to afford the price and heavy elemental contaminations. There is a strong desire to develop low-toxicity, highly luminescent NCs with larger Stokes shifts and improved stability, in particular, low cost, to compete with rare earth-based phosphors. The available high-quality CIZS NCs are expected to fit the requirements. This motivates intensive investigations into the use of CIZS NCs as potential alternatives for color-converting materials. In addition to the materials optimization, there are also considering efforts on the configuration design of the devices. Most of the primary results concern on the “on-chip”-type devices. Table 1 summarize the progress toward this target. It has been proved that the optimized WLED devices with CIZS NCs have comparative luminous efficiency but show better color quality with an improved color rendering index up 438



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Figure 5. (a) Schematic presentation of device fabrication for fabricating CuInS2 NC-based LEDs. (b) EL spectra of the device with changing voltage. (c) EQE plots (d) device schematic of a multilayered QLED and (e) EL spectra of a QD-based device with increasing driving voltage (f) Current efficiency and EQE as a function of luminance of three QLEDs integrated with CuInS2 NCs with different emission wavelengths. Panels (a− c) are adopted from ref 89, and panels (d−f) are from ref 125.

the charge injection and carrier recombination. Figure 5e presents the EL at different voltages, and Figure 5f shows the EQE percentage of the device (details in the figure caption). With the development of single-color devices, integration into white light has also been illustrated. The first whiteemitting device was based on a mixture of CIZS NCs and conjugated polymer, with decent performance.126 This was later optimized by using another polymer.129 In recent works, white light is also achieved by mixing blue-emitting CdZnSe/ZnS NCs with red-emissive CIZS NCs (Figure 6a) in the emissive layer.128 In other works, as illustrated in Figure 6b,c, the color temperature could be tuned by varying the driving voltage as well as the ratio between the blue- and red-emissive materials. More impressively, white light is observed on the devices based on single-component CuGaS2-based NCs by finely tuning the material structures (see Figure 6d).130 Recently, Mn-doped ternary NCs were also developed to bring white light emission.129 For Mn d−d emission, the host needs to have high-bandgap semiconductor. Ideally, in a multinary system, significant Zn is incorporated to widen the bandgap and facilitate an efficient host exciton energy in Mn dstates. Recently, white light emission was obtained by doping Mn in CuGaS2 with an alloy and shell with ZnS (CZGS). Figure 7a shows the PL spectra with different Mn and Cu ratios in CZGS NCs. Interestingly, doping Mn to these ternary NCs results in ∼600 nm Mn d−d emission, a red shift emission compared to the traditional Mn emission. This indeed helped provide an ideal platform to bring the red part of the visible spectrum to contribute to the intense white light. Depending on the Mn concentration, the intensity of the CGZS defect state and Mn d−d emissions are tuned. With an increase in the intensity of Mn d−d emission, the ternary blue emission

and a few display panel demos (4 in. size or larger) have been successfully demonstrated.119,120 However, the devices based on Cd free NCs greatly lag behind the well-developed CdSe NCs.121 Table 2 summarizes the progress of I−III−VI NCbased EL devices. It is noted that the improvement of device performance mainly relies on the materials optimizations. Here we would like to highlight two recent achievements in LED fabrications. As shown in Figure 5a−c, efficient and bright lightemitting diodes were recently demonstrated by adopting an inverted structure of ITO/ZnO/QDs/CBP/TCTA/MoO3/Al using hydroxyl-terminated alcohol-soluble CuInS2-based NCs as an emitting layer. The optimized devices showed a maximum luminance of 8375 cd/m2 and an external quantum efficiency (EQE) of 3.22%.89 The performance enhancement could be

The performance enhancement could be explained by considering the decreased energy barriers between the electron transport layer and the emitting layer. explained by considering the decreased energy barriers between the electron transport layer and the emitting layer. Figure 5a shows the schematics of the device layers, Figure 5b presents the EL under different voltages, and Figure 5c depicts the EQE percentage of the device. In another work, Yang et al. report the fabrication of CIZS NC-based EL devices with a current efficiency of 18.2 cd/A and EQE of 7.3% using a conventional device structure of ITO/PEDOT:PSS/TFB/QDs/ZnO/Al (Figure 5d).125 The performance improvement was mainly attributed to the shell thickness control, which correlated with 439



Perspective

Figure 6. (a) Schematic white LED device structure with CIS/ZnS as the emitting layer. (b) Typical emission spectra of the devices with different volume ratios (CIS/ZnS: ZnCdSe/ZnS), all at a 9 V operation voltage. (c) Position of the emission spectra of the mono- and bichromatic devices at 9 V within the CIE 1931 color space with respect to the blackbody radiator curve.128 (d) Device schematic of a CGS/ZnS-based multilayered white QLED, (e) as-collected EL spectra, and (f) the corresponding variation of CIE color coordinates of a white EL as a function of applied voltage.129

Figure 7. (a) PL spectra of Mn-doped CuGaS2/ZnS (CGZS) NCs with Mn to Cu ratio variations. (b) EL spectra showing the cool-to-warm shifting in the white light LEDs. (c) Color index coordinates of Mn-doped CGHS. Panels of this figure are adopted from ref 130.

efficiencies, and performance are also stated. However, there are several issues that still remain unsolved, and also, more studies on these materials for device applications are required. Here are some future prospects of these materials that might be explored for widespread applications. (1) Advanced synthesis of ternary NC emitters for large-scale production without compromising the quality is still a challenge, and hence, optimizing the reactions beyond the laboratory scale is a timely requirement. To achieve this target, deep insight into the chemical synthesis is very nessessary.129−131 (2) From the viewpoint of fundamental science, the lack of precise size and composition control still limits the understanding of their size- and compositional-dependent optical properties. A comprehensive single-dot

simultaneously decreased, providing a control over tuning the intensity of white light from the cool to warm window. Figure 7b presents corresponding EL spectra in the devices. Insets in both cases present the digital images of restive solutions and devices under illumination and dc supply, respectively. Figure 7c presents the CIE coordinates for generating white light in composition variations. Summary and Future Prospects. In summary, recent developments of light-emitting ternary I−III−V semiconductor NCs from large-scale synthesis to device applications are discussed. The gram scale synthesis that is typically required for commercialization of the material, surface modifications with different ligands that are required for dispersing the NCs in different media, tuning the emission windows by tuning the composition/size, and doping to obtain white light emission are also discussed. Model devices for white light EL, their 440



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(4)

(5)

(6)

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characterization and spectroscopic measurement are very desired to clarify the correlations between their optical properties and the physical parameters.132−135 Toward color-converted LED applications, remote-type devices seem more promising. The most concerning problem is the PL quenching effect during the embedding process and under light excitation.136 In this direction, it is important to address both the thermally induced physical quenching and thermally induced chemical oxidation processes. Future device applications should be correlated with printing techniques. Considering this, it is of great interest to develop advanced surface modulations using suitable ligands for dispersion in different solvents, and hence, appropriate ligands preferably with short chain organics at high operation temperature are required. A single system with manipulation of the composition for generating intense white light is also in demand for white light LEDs. This would reduce the complexity of mixing or selecting other materials emitting in a different spectral window. This can be modeled by composition variation bandgap engineering or doping appropriate optically active dopants. The rising challenge will be how to design materials with white light emission and process them into devices.124 Although the CIZS NC-based EL device achieved great progress, the performance is still far behind the expectation for white lighting applications. To push forward the device work, understanding the working mechanism and investigating more device fabrications are important, which might be different with that for welldeveloped CdSe NCs. It is possible to design better hole and electron transport layers to improve the performance. Moreover, the combination of versatile surface modifications with EL devices also might evoke the investigation of chemically and biologically sensitive devices.

Dr. Narayan Pradhan is currently working as a Professor in the Department of Materials Science at Indian Association for the Cultivation of Science, Kolkata, India. His research interest is in investigating the chemistry and physics of semiconductor nanomaterials. He received his Ph.D. degree from IIT Kharagpur and continued his post doc at Ben-Gurion University, Israel and the University of Arkansas, U.S.A. Currently, he is serving as senior editor for The Journal of Physical Chemistry A/B/C. He has been awarded the Oxford Instruments Young Nanoscientist, DST-India young career award in Nanoscience, LNJ Bhilwara Research Fellow in Nanoscience, and DST-India Swarnajayaniti Fellowship in Chemistry. His research is focused on the physics and chemistry of semiconductor nanomaterials. Dr. Haizheng Zhong is currently working as a full Professor of Photonic Materials in the School of Materials Science & Engineering at Beijing Institute of Technology (BIT), Beijing, China. He received his Ph.D. degree from the Institute of Chemistry of Chinese Academy of Sciences (ICCAS) and spent 6 months at the University of California, Los Angeles (UCLA) as a visiting student. After his Ph.D., he continued his post doc at the University of Toronto, Canada. His research interests are in the area of quantum dots for light-based technology. His achievements focus on emerging low-cost quantum dots (CuInS2, CuInSe2, and halide pervoskites) for lighting and display applications.

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ACKNOWLEDGMENTS H.Z. and B.C. acknowledge the funding support of the Natural Science Foundation of China (Nos. 61735004, 21573018, 51602024); N.P. acknowledges the DST (Swarnajayanti, DST/ SJF/CSA-01/557 2010-2011), Govt of India and a BIT shortterm visiting professorship.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (H.Z.). *E-mail: [email protected] (N.P.). *E-mail: [email protected] (B.C.). ORCID

Narayan Pradhan: 0000-0003-4646-8488 Haizheng Zhong: 0000-0002-2662-7472 Notes

The authors declare no competing financial interest. Biographies Dr. Bingkun Chen is currently working as an assistant professor in the School of Optics and Photonics at Beijing Institute of Technology (BIT), Beijing, China. He received his Ph.D. in materials science at BIT (supervisors: Prof. Bingsuo Zou and Prof. Haizheng Zhong) in 2013. After his Ph.D. period, he worked with Prof. Yongtian Wang (BIT) and Prof. Andrey Rogach (City Uiversity of Hongkong) of “Hong Kong postdoctoral scholarship” during 2014−2016. In June 2017, he joined the laboratory of the Beijing Engineering Research Center of Mixed Reality and Advanced Display at BIT as a tenuretrack faculty. His current research interests focus on functional oxidebased nanomaterials for optoelectronics. 441



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