Saponification Precipitation Method of CsPbBr3 Nanocrystals with

Subscriber access provided by YORK UNIV

C: Plasmonics; Optical, Magnetic, and Hybrid Materials

Saponification Precipitation Method of CsPbBr3 Nanocrystals with Blue-Green Tunable Emission Gopi C. Adhikari, Preston A. Vargas, Hongyang Zhu, and Peifen Zhu J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b10636 • Publication Date (Web): 03 Dec 2018 Downloaded from http://pubs.acs.org on December 4, 2018

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 21 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 Journal of Physical Chemistry

Saponification Precipitation Method of CsPbBr3 Nanocrystals with Blue-Green Tunable Emission Gopi C. Adhikari,‡ Preston A. Vargas,‡ Hongyang Zhu, and Peifen Zhu * Department of Physics and Engineering Physics, The University of Tulsa, Tulsa, Oklahoma, 74104, United States

1 ACS Paragon Plus Environment

The Journal of Physical Chemistry 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: We report on a new synthesis process for halide perovskite nanoplatelets and nanoplates that switches the production process of the cesium precursor from a fatty acid/cesium salt reaction to a cesium base/fatty acid ester reaction, thus enabling the reaction to occur in ambient conditions in minutes instead of hours. The saponification precipitation process reported here, as a result, does not require a vacuum oven or inert reaction environment in obtaining the cesium precursor, or any part of the reaction. Furthermore, the process creates a hygroscopic byproduct that results in a self-drying synthesis. The obtained perovskite nanocrystals exhibit a blue-green tunable emission that occurs via quantum confinement effect, phase, and morphology change. The consequence of these physical processes is that the band gap is highly tunable with temperature and the resulting nanocrystals show remarkable optical properties, while greatly simplifying the production of halide perovskite nanoplatelets and nanoplates.


Page 2 of 21

Page 3 of 21 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


INTRODUCTION Inorganic lead halide perovskite nanocrystals have attracted tremendous attention in recent years due to their remarkable properties such as tunable and narrow linewidth emission and high quantum yield.1-7 These properties lead to potential applications in optoelectronic devices such as light-emitting diodes (LEDs),8-11 lasers,12-13 solar cells,14-16 high-quality displays,17-19 and photodetectors.20-21 In the past few years, various synthesis processes have been reported towards the application of these materials in the new generation of optoelectronic devices. Protesescu et al. synthesized CsPbX3 (X-halides) nanocrystals by employing a hot-injection method in 2015.22 While the high-quality nanocrystals were obtained, the reaction of cesium salts (Cs2CO3) and a fatty acid (oleic acid) only takes place at high temperatures, which would result in the oxidation of reactants. Thus, a vacuum oven or inert atmosphere is required to prevent the oxidation. These requirements severely hamper the feasibility of applying this method on a large scale. Other methods such as solvothermal,23-24 supersaturated recrystallization,17 chemical vapor deposition,25 ultrasonication,26-27 microwave-assisted,28 mechanosynthesis,29 vacuum deposition,30 and microchannel reactor methods 31 have also been reported to accommodate different purpose. The use of these methods has either achieved desirable material qualities but compromised the cost or lowered the production cost but compromised material qualities. Therefore, further exploration of low-cost and large-scale approaches for synthesizing perovskite nanocrystals are required to realize the applications of these materials in modern devices. In this work, a low-cost and facile saponification precipitation process was developed to synthesize CsPbBr3 nanoplatelets and nanoplates with uniform size distribution. By using CsOH and glyceryl trioleate, the reaction is reversed to a cesium base and fatty acid ester reaction from a fatty acid and cesium salt reaction. Since alkaline hydroxides are such strong bases, the reaction



occurs almost immediately under ambient conditions. Thus, this process does not require any high temperature, special apparatus, and vacuum or inert atmosphere to obtain Cs-oleate precursor solutions in minutes instead of hours. This is not the first time that an alternate cesium compound was used to this effect,32 but the hydroxide and glyceryl groups involved provide specific benefit that is absent from other synthesis processes. The reaction used to produce the cesium precursor yields glycerol. Glycerol, otherwise known as glycerine, is a highly hygroscopic compound.33-34 When present during the rest of the synthesis process, it will act as a drying agent. This will protect halide perovskite precursors from the effects of moisture during synthesis, but the benefit is lost when the products are separated. The effects of glycerol on protecting as-synthesized perovskites may be a subject of future work. The tunable emission of these halide perovskite nanocrystals (460 nm - 530 nm) was obtained by varying reaction temperature (8 oC - 150 oC). This process is also feasible for both chloride and iodide perovskites, because the hydroxide compound introduced here only reacts to form the cesium precursor and glycerol. Glycerol is inert to this reaction. The simplification of both general fabrication and emission tuning described herein provides an approachable pathway for applications of this material in optoelectronic devices with inherent protection from moisture.

EXPERIMENTAL SECTION CHEMICALS The chemicals used to synthesize CsPbBr3 nanoplatelets and nanoplates are lead (II) bromide (PbBr2, Alfa Aesar, 98%), dimethylformamide (DMF, ACROS Organics, 98%), cesium hydroxide monohydrate (CsOH, Santa Cruz Biotechnology, 99.9%), glyceryl trioleate (C57H104O6, Chem Cruz, 65%), octadecene (ODE, ACROS Organics, 90%, technical grade), oleylamine (OM,


Page 4 of 21

Page 5 of 21 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


Aldrich, 70%), oleic acid (OA, Alfa Aesar, 90%), acetone (CAROLINA), and toluene (Fisher Chemical, 99.9%). All chemicals were used without any further purification.

Figure 1. Schematic diagram of the saponification reprecipitation synthesis process. EXPERIMENTAL PROCEDURE The details of saponification reprecipitation process are illustrated in Figure 1. First, an equimolar ratio of CsOH (0.2 g) and glyceryl trioleate (0.433 mL) was mixed in a beaker along with 3 mL of an ODE to obtain a 0.4 M Cs-oleate precursor. 0.4 M PbBr2 was obtained by adding 0.735 g of PbBr2 into 5 mL of DMF. 0.04 mL of Cs-oleate precursor (~ 100 oC) was added to a mixture of 2.5 mL of the ODE, 0.25 mL of OM, and 0.25 mL of OA with stirring. Then, 0.4 mL of PbBr2 was dropped into that solution at a desired growth temperature (8 oC - 150 oC). 10 mL of acetone was added into the flask to accelerate the reaction and a colloidal suspension was obtained. The nanocrystals were collected by discarding the supernatant after centrifuged the colloidal suspension at 1000 rpm for 5 minutes. All experiments were performed under an ambient 5 ACS Paragon Plus Environment


atmosphere. Note that the Cs-oleate was obtained by using CsOH and glyceryl trioleate instead of Cs2CO3 and oleic acid, which were used in the hot injection method. This reaction is reversed to a strong base reaction instead of a weaker acid reaction and occurs almost immediately upon contact between CsOH and glyceryl trioleate. The addition of acetone forced the nucleation of nanocrystals. The use of this new saponification precipitation will lead to significant cost reduction.

CHARACTERIZATION For the study of structural properties of nanocrystals, X-ray diffraction (XRD) measurements were carried out by using Rigaku Smart Lab with Cu Kα1 radiation, λ =1.54 Aͦ operating at 40 kV and 44 mA. Transmission electron microscopy (TEM) observations were performed using a Hitachi H-7000 TEM at 75 kV. The optical properties were analyzed by the measurement of absorption and photoluminescence (PL) spectra using A VARIAN Carry 50 Scan UV- Spectrophotometer, and A Spectro-Fluorophotometer (Shimadzu, RF-6000) with a xenon lamp as an excitation source, respectively.

RESULTS AND DISCUSSION XRD patterns (Figure 2) were measured to investigate the effect of growth temperature on the structural properties of obtained samples. The nanocrystals synthesized at the lower temperatures (8 oC, 20 oC, and 90 oC) exhibited the main characteristic peaks of the cubic perovskite crystal structure.35 The main peaks are at ~ 15° and 30°, and 45°, which are assigned to the (100), (200) and (300) planes, respectively. However, there is evidence that CsPbX3 always exhibit an orthorhombic phase at the unit cell level.36 The opposed orthorhombic subdomains of the nanocrystal annihilate their superstructural peaks leading to a perceived cubic phase that is in 6 ACS Paragon Plus Environment

Page 6 of 21

Page 7 of 21 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 2. XRD patterns of CsPbBr3 perovskites grown at the various synthesis temperatures. reality pseudocubic.37 The diffraction peaks shifted slightly to higher diffraction angles with increasing reaction temperature, which indicates a gradual shrinking of the unit cell. When the temperature increased to 110 oC, the peaks due to the diffraction of (004) and (220) planes started to appear as shown in Figure 2. These peaks are attributed to the octahedral subdomains of the nanocrystals no longer hiding their superstructural peaks and reveal planes of the orthorhombic structure.38-40 It is possible that the increased synthesis temperatures cause the octahedra to align more prevalently. The peaks due to the planes (004) and (220) became more discrete when the temperature further increased to 150 oC, which indicates the further coordination of octahedral subdomains. Thus, the crystal structure can be engineered by the reaction temperature. Contrary to expected behavior, the XRD peaks narrowed with decreasing nanocrystal size. This is explained by surface defects becoming more common in higher temperature syntheses, resulting in XRD peaks broadening. This effect is demonstrated in the reverse direction by surface defect repair.41



Also, the presence of low-angle peaks in the diffraction patterns for these nanocrystals indicates the presence of superlattice constructs.3, 42

Figure 3. TEM images of CsPbBr3 nanocrystals grown at the different synthesis temperatures as indicated. TEM measurements were carried out to study the effect of temperature on the morphology of these nanocrystals, which are shown in Figure 3. The nanocrystals grown at 8 oC loosely form undirectionally aligned nanoplatelets (Figure 3 a). The thickness of these broken nanoplatelets is on the order of a single unit cell. The breaks in nanoplatelet structure indicate that nanoplatelets are constituted of individual quantum dots. Substantially more organized nanoplatelets structures were obtained when temperature increased to 20 oC (Figure 3 b). The stacking of nanoplatelet structure continues as the temperature further increased to 90 oC (Figure 3 c). Note that the nanoplatelets grown at 20 oC are markedly thinner (∼ 1.1 nm, approximately 2 unit cells) than those grown at 90 oC (∼ 3 nm, corresponding to 5 unit cells). The increase in size of nanoplatelets lead to the


Page 8 of 21

Page 9 of 21 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


lattice contraction as shown in Figure 2. At the temperatures of 110 oC or above, monodisperse nanoplates were formed instead of the nanoplatelets. These nanoplates have an average side length of 10 nm at 110 oC (Figure 3 d). This corresponds to approximately 170 unit cells across. As the synthesis temperature increased to 150 oC, the nanoplates grew larger with the average side length of 13 nm (see Figure 3 e), which is nearly 222 unit cells across. These structures cluster less coherently than the nanoplatelets. This unordered clustering of structures may be a result of the higher synthesis temperature, which increases the energy available in the reaction environment, thereby encouraging less organized growth patterns. The nanoplates synthesized at 150 oC appear darker in TEM images than the nanoplates grown at 110 oC, which indicates that thicker nanoplates were obtained at higher temperatures. The size and morphology engineering was achieved by varying the reaction temperature during saponification reprecipitation process.



Figure 5. The bandgap of CsPbBr3 as a function of synthesis temperature. The shift in bandgap Figure 4. The absorption spectra of CsPbBr3 nanocrystals grown at different synthesis near 100 oC indicates a shift in the apparento phase of the nanocrystals. temperatures. Inset is the Tauc plot of 150 C sample. The absorption spectra were measured to study the effect of temperature on the band gap of these nanocrystals. Figure 4 shows effective absorption of these nanocrystals through UV-visible range. The band gap of this material was tuned by changing the synthesis temperature. For lower temperature range (≤ 90 oC), the peak in the absorption spectrum is attributed to exciton absorption. The peak is red-shifted with increasing temperature owing to the gradual loss of quantum confinement as a result of the growth of thicker nanoplatelets.43-44 The parasitic absorption shown in Figure 4 at wavelengths beyond the exitonic line comes from free-carrier absorption.45 The corresponding band gap was approximated from the peak of the absorption spectra for temperature ≤ 90 oC and using Tauc plot (inset of Figure 4) for > 90 oC, shown in Table 1. When the temperature further increased beyond 90 oC, a dramatic band gap change was observed at 100 oC. At 110 oC, the [PbBr6]4+ octahedral subdomains began to show their superstructural peaks as the octahedral tilting began to face the same direction, which resulted in the overt orthorhombic crystal structure as shown in Figure 2 and the decreased band gap. The band gap continuously decreased with 10 ACS Paragon Plus Environment

Page 10 of 21

Page 11 of 21 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


further increase in synthesis temperature up to 150 oC. Hence, the band gap is tunable from 2.83 eV to 2.21 eV. The band gap as a function of temperature is plotted in Figure 5. A dramatic band gap change observed at ~100 oC is related to an apparent phase transition from pesudocubic to orthorhombic. A lattice distortion in the perovskite leads to a band gap shrink. Note that the change in temperature resulted in the crystal size change, crystal structure change, lattice distortion, and morphology change. All of these contributed to band gap engineering.

Figure 6. The normalized emission spectra of CsPbBr3 nanocrystals (excited at 361 nm) synthesized at different temperatures. The peak emission is being red shifted with increasing synthesis temperature. The normalized PL emission spectra of CsPbBr3 nanocrystals synthesized at different temperatures under consistent excitation wavelength (361 nm) are shown in Figure 6. The emission peak is red shifted from 460 nm to 530 nm by increasing the temperature. This shift appears alongside a change in the size, structure and morphology of the nanocrystals. The stability is on par with other synthesis methods in the literature,46 as it has remained stable in colloidal suspension for months without significant change in photoluminescence. The peak emission wavelengths at a corresponding temperature are summarized in Table 1. The peak emission wavelength gradually 11 ACS Paragon Plus Environment


Page 12 of 21

Table 1. The bandgap, peak emission wavelength, and FWHM at different synthesis temperatures. Synthesis

Band

Peak

FWHM

temperature

gap

wavelength

(nm)

(oC)

(eV)

(nm)

8

2.83

460

18.7

20

2.78

466

15.9

90

2.69

478

23.9

110

2.27

515

23.5

150

2.21

530

22.0

increased from 460 nm to 478 nm with the increase in temperature from 8 oC to 90 oC. This is attributed to the quantum confinement effect caused by the change in size of nanocrystals with temperature, shown in Figure 3. The thickness of nanoplatelets increased with the increase in temperature. The low energy tail on the emission, while normally indicative of inconsistent nanocrystal size, is in this case a result of reabsorption as demonstrated by Weerd et al.47 as the nanocrystal sizes are largely homogeneous. The large red shift in peak emission wavelength from 90 oC to 110 oC is due to the apparent phase change from pseudocubic to orthorhombic (Figure 2) as well as morphology change from nanoplatelets to nanoplates (Figure 3). The auxiliary emission peak that arises from a 110 oC synthesis temperature is a result of an incomplete transformation from nanoplatelet formation to nanoplate formation (Figure 3). The incomplete transformation past the critical temperature may be due to temperature inconsistencies that result from using acetone as the anti-solvent for the reaction. Acetone’s low boiling point prevents it from being combined


Page 13 of 21 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


with the solution at higher reaction temperatures without causing substantial temperature gradients. This effect also accounts for the emission tail at the temperature of 150 oC. The further red shift of emission from 110 oC to 150 oC is due to the change in nanocrystal size. Note that the tunable emission was obtained by tuning synthesis temperature, which is attributed to the temperature induced crystal size change, phase change, morphology change, and lattice contraction. Therefore, the material properties were engineered by the synthesis temperature. The XRD patterns, TEM images, absorption spectra, and band gap vs. synthesis temperature graph also confirm the presence of a critical temperature. The nanocrystals synthesized at 110 oC changed from pseudocubic phase to orthorhombic phase, from nanoplatelets to nanoplates, and single absorption peak to broadband absorption form. Furthermore, there is a dramatic drop in the band gap energy beyond a synthesis temperature of 90 oC. Note that the synthesis temperatures were limited between 8 oC and 150 oC because the emission spectra do not vary significantly beyond this temperature range and oxidation effects become an issue for the reactants at higher temperatures.



Page 14 of 21

The full-width at half-maximum (FWHM) of the emission spectra was calculated and summarized in Table 1. The narrow line-width emission was obtained which indicates that the obtained nanocrystals are very uniform and generated a consistent emission.48 Also, this narrow line width is the characteristic of and high color purity.3,

49

Thus this process is capable of

producing nanocrystals of similar color quality to hot injection methods.

Figure 7. The normalized excitation spectra of CsPbBr3 nanocrystals synthesized at different temperatures. The excitation broadband spectra lie in the emission range of III-nitride UV/blue LED. The normalized excitation spectra of CsPbBr3 nanocrystals synthesized at different temperatures are shown in Figure 7. The excitation spectra were measured by monitoring the corresponding peak emission wavelength shown in Figure 6. These spectra have a broadband shape from UV to blue, which indicates that these perovskites can be excited by a wide range of wavelengths. The excitation range of CsPbBr3 lies in the range of emission by the III-nitride UV/blue LEDs. The temperature dependent tunability of emission spectra indicate that CsPbBr3 nanocrystals are capable of emitting over a wide span of the visible spectrum from blue to green. Thus, the nanocrystals grown under this greatly simplified process are favorable for use as photon down 14 ACS Paragon Plus Environment

Page 15 of 21 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


converter in conjunction with III-nitride based UV/blue LEDs to generate white light emission with a desirable color quality. This will solve the issues facing in the current generation of white LEDs. The white LEDs on market are produced by coating the yellow phosphors (YAG: Ce3+) on high efficient III-nitride UV/ blue LEDs.50-53 However, the high correlated color temperature (CCT ~ 6000 K) and low color rendering index (CRI < 75 %) due to the lack of green and red colors are undesirable for indoor lighting applications.54 In addition, the limited material availability of the rare earth elements used in conventional down conversion phosphors increases the initial cost.55 Coating UV LEDs with blue, green, and red phosphors or coating blue LEDs with green and red phosphors is one of the most promising approaches for achieving white LEDs with desired CCT and high color quality.54,

56-57

However, the low efficiency of green LEDs caused by

fundamental phase separation issue in the high Indium content InGaN quantum well layer is a barrier to get warm and high efficient white LEDs.58 Therefore, the combination of earth abundant elements and low-cost and large-scale approaches for obtaining high efficiency photon down conversion materials is solution for achieving high-efficient and economic white LED with desired CCT and superior color quality. The tunable and narrow line width emission was obtained from CsPbBr3 nanocrystals by employing new, facile, low-cost, and large-scale saponification reprecipitation method. This will speed up the application of these new materials in white LED industry. Nanocrystals synthesized at lower temperatures (≤ 90 oC) are shown to be small enough to experience quantum confinement effects, which becomes weaker for larger nanocrystals synthesized at higher temperatures. Therefore, the band gap of the perovskite nanocrystals decreased with increasing synthesis temperature for lower temperature samples. As the synthesis temperature increased above 90 oC, the increased energy in the reaction environment caused a



change in the structural preference and morphology of the nanocrystals from pseudocubic nanoplatelets to orthorhombic nanoplates. This also had the effect of increasing the dimensions of the nanocrystals to beyond that of the Bohr radius for the material. Therefore, the quantum confinement effect was no longer applicable to explain the further decreasing band gap with further increasing temperature. Coordination of octahedra tilting caused the continued decrease in band gap energy. This directional alignment of octahedral tilting can clearly be seen in the XRD patterns of the higher synthesis temperature samples and was simply hidden in lower synthesis temperatures. The tilting coordination led to the phase change from pseudocubic to orthorhombic.

CONCLUSIONS In summary, the production of halide perovskite nanocrystals has been substantially simplified by the new saponification precipitation method. This method has proven capable of being used to produce halide nanocrystals that have comparable optical properties to nanocrystals produced by the hot injection method, while also being much easier to enact. By reversing the cesium precursor production process such that it may occur in ambient conditions, the need for vacuum ovens and inert atmospheres was removed. Furthermore, the lack of advanced apparatuses used in the process as a whole greatly increased the potential scalability of this process. It was also determined, however, that the band gap tuning due to synthesis temperature variation was a product of a few separate physical processes. The tunable size of nanocrystals as a result of quantum confinement was responsible for the decrease of band gap with increasing synthesis temperature, while phase and morphology change as well as lattice distortion caused further decrease of the band gap. Thus, this process is not only simpler than other methods; it also exhibits multiple band gap tuning modes within the adjustment of synthesis temperature alone. Moreover, the resulting by-product glycerol 16 ACS Paragon Plus Environment

Page 16 of 21

Page 17 of 21 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


is nonreactive to the remainder of the method, but is strongly hygroscopic, therefore drying the other reactants, which helps to stabilize the samples.

AUTHOR INFORMATION Corresponding Author *Email:

[email protected]. Phone: +1 (918) 631-5125

Authors Contributions ‡ These

authors had equal contributions.

Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS The authors acknowledge the financial supports in part by The University of Tulsa through a Startup Fund, in part by The University of Tulsa Faculty Development Summer Fellowship. The authors would like to acknowledge Dr. Parameswar Harikumar’s help with absorption measurements and Dr. Alexei Grigoriev’s help with XRD measurements.

REFERENCES (1) Song, L.; Guo, X.; Hu, Y.; Lv, Y.; Lin, J.; Liu, Z.; Fan, Y.; Liu, X. Efficient Inorganic Perovskite Light-Emitting Diodes with Polyethylene Glycol Passivated Ultrathin CsPbBr3 Films. J. Phys. Chem. Lett. 2017, 8, 41484154. (2) Song, J.; Li, J.; Li, X.; Xu, L.; Dong, Y.; Zeng, H. Quantum Dot Light-Emitting Diodes Based on Inorganic Perovskite Cesium Lead Halides (CsPbX3). Adv. Mater. 2015, 27, 7162-7167. (3) Adhikari, G. C.; Zhu, H.; Vargas, P. A.; Zhu, P. UV-Green Emission from Organolead Bromide Perovskite Nanocrystals. J. Phys. Chem. C 2018, 122, 15041-15046. (4) Bekenstein, Y.; Koscher, B. A.; Eaton, S. W.; Yang, P.; Alivisatos, A. P. Highly Luminescent Colloidal Nanoplates of Perovskite Cesium Lead Halide and Their Oriented Assemblies. JACS 2015, 137, 1600816011. (5) Chang, S.; Bai, Z.; Zhong, H. In Situ Fabricated Perovskite Nanocrystals: A Revolution in Optical Materials. Adv. Opt. Mater. 2018, 6, 1800380. (6) Zhu, H.; Cai, T.; Que, M.; Song, J.-P.; Rubenstein, B. M.; Wang, Z.; Chen, O. Pressure-Induced Phase Transformation and Band-Gap Engineering of Formamidinium Lead Iodide Perovskite Nanocrystals. J. Phys. Chem. Lett. 2018, 9, 4199-4205. 17 ACS Paragon Plus Environment


(7) Nagaoka, Y.; Hills-Kimball, K.; Tan, R.; Li, R.; Wang, Z.; Chen, O. Nanocube Superlattices of Cesium Lead Bromide Perovskites and Pressure-Induced Phase Transformations at Atomic and Mesoscale Levels. Adv. Mater. 2017, 29, 1606666. (8) Penning, J.; Stober, K.; Taylor, V.; Yamada, M. Energy Savings Forecast of Solid-State Lighting in General Illumination Applications. Washington, D.C. 2016, 1-101. (9) Jizhong, S.; Jianhai, L.; Xiaoming, L.; Leimeng, X.; Yuhui, D.; Haibo, Z. Quantum Dot Light-Emitting Diodes Based on Inorganic Perovskite Cesium Lead Halides (CsPbX3). Adv. Mater. 2015, 27, 7162-7167. (10) Shimizu, K. T.; Böhmer, M.; Estrada, D.; Gangwal, S.; Grabowski, S.; Bechtel, H.; Kang, E.; Vampola, K. J.; Chamberlin, D.; Shchekin, O. B., et al. Toward Commercial Realization of Quantum Dot Based White Light-Emitting Diodes for General Illumination. Photon. Res. 2017, 5, A1-A6. (11) Chen, X.; Zhang, F.; Ge, Y.; Shi, L.; Huang, S.; Tang, J.; Lv, Z.; Zhang, L.; Zou, B.; Zhong, H. CentimeterSized Cs4PbBr6 Crystals with Embedded CsPbBr3 Nanocrystals Showing Superior Photoluminescence: Nonstoichiometry Induced Transformation and Light-Emitting Applications. Adv. Funct. Mater. 2018, 28, 1706567. (12) Fu, Y.; Zhu, H.; Schrader, A. W.; Liang, D.; Ding, Q.; Joshi, P.; Hwang, L.; Zhu, X. Y.; Jin, S. Nanowire Lasers of Formamidinium Lead Halide Perovskites and Their Stabilized Alloys with Improved Stability. Nano Lett. 2016, 16, 1000-1008. (13) Deschler, F.; Price, M.; Pathak, S.; Klintberg, L. E.; Jarausch, D.-D.; Higler, R.; Hüttner, S.; Leijtens, T.; Stranks, S. D.; Snaith, H. J., et al. High Photoluminescence Efficiency and Optically Pumped Lasing in Solution-Processed Mixed Halide Perovskite Semiconductors. J. Phys. Chem. Lett. 2014, 5, 1421-1426. (14) Yang, S.; Fu, W.; Zhang, Z.; Chen, H.; Li, C.-Z. Recent Advances in Perovskite Solar Cells: Efficiency, Stability and Lead-Free Perovskite. J. Mater. Chem. A 2017, 5, 11462-11482. (15) Wang, Q. Fast Voltage Decay in Perovskite Solar Cells Caused by Depolarization of Perovskite Layer. J. Phys. Chem. C 2018, 122, 4822-4827. (16) Khadka, D. B.; Shirai, Y.; Yanagida, M.; Miyano, K. Degradation of Encapsulated Perovskite Solar Cells Driven by Deep Trap States and Interfacial Deterioration. J. Mater. Chem. C 2018, 6, 162-170. (17) Xiaoming, L.; Ye, W.; Shengli, Z.; Bo, C.; Yu, G.; Jizhong, S.; Haibo, Z. CsPbX3 Quantum Dots for Lighting and Displays: Room-Temperature Synthesis, Photoluminescence Superiorities, Underlying Origins and White Light-Emitting Diodes. Adv. Funct. Mater. 2016, 26, 2435-2445. (18) Sifei, Z.; Jingfang, Z.; Yanmei, S.; Yi, H.; Bin, Z. Self-Template-Directed Synthesis of Porous Perovskite Nanowires at Room Temperature for High-Performance Visible-Light Photodetectors. Angew. Chem. Int. Ed. 2015, 54, 5693-5696. (19) Zhang, F.; Zhong, H.; Chen, C.; Wu, X.-g.; Hu, X.; Huang, H.; Han, J.; Zou, B.; Dong, Y. Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology. ACS Nano 2015, 9, 4533-4542. (20) Sutherland, B. R.; Johnston, A. K.; Ip, A. H.; Xu, J.; Adinolfi, V.; Kanjanaboos, P.; Sargent, E. H. Sensitive, Fast, and Stable Perovskite Photodetectors Exploiting Interface Engineering. ACS Photonics 2015, 2, 11171123. (21) Deng, H.; Yang, X.; Dong, D.; Li, B.; Yang, D.; Yuan, S.; Qiao, K.; Cheng, Y.-B.; Tang, J.; Song, H. Flexible and Semitransparent Organolead Triiodide Perovskite Network Photodetector Arrays with High Stability. Nano Lett. 2015, 15, 7963-7969. (22) 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, 36923696. (23) Chen, M.; Zou, Y.; Wu, L.; Pan, Q.; Yang, D.; Hu, H.; Tan, Y.; Zhong, Q.; Xu, Y.; Liu, H., et al. Solvothermal Synthesis of High-Quality All-Inorganic Cesium Lead Halide Perovskite Nanocrystals: From Nanocube to Ultrathin Nanowire. Adv. Funct. Mater. 2017, 27, 1701121. 18 ACS Paragon Plus Environment

Page 18 of 21

Page 19 of 21 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


(24) Zhai, W.; Lin, J.; Li, Q.; Zheng, K.; Huang, Y.; Yao, Y.; He, X.; Li, L.; Yu, C.; Liu, C., et al. Solvothermal Synthesis of Ultrathin Cesium Lead Halide Perovskite Nanoplatelets with Tunable Lateral Sizes and Their Reversible Transformation into Cs4PbBr6 Nanocrystals. Chem. Mater. 2018, 30, 3714-3721. (25) Aamir, M.; Sher, M.; Khan, M. D.; Malik, M. A.; Akhtar, J.; Revaprasadu, N. Controlled Synthesis of All Inorganic CsPbBr2I Perovskite by Non-Template and Aerosol Assisted Chemical Vapour Deposition. Mater. Lett. 2017, 190, 244-247. (26) Tong, Y.; Bladt, E.; Aygüler, M. F.; Manzi, A.; Milowska, K. Z.; Hintermayr, V. A.; Docampo, P.; Bals, S.; Urban, A. S.; Polavarapu, L., et al. Highly Luminescent Cesium Lead Halide Perovskite Nanocrystals with Tunable Composition and Thickness by Ultrasonication. Angew. Chem. Int. Ed. 2016, 55, 13887-13892. (27) Tong, Y.; Bohn, B. J.; Bladt, E.; Wang, K.; Müller-Buschbaum, P.; Bals, S.; Urban, A. S.; Polavarapu, L.; Feldmann, J. From Precursor Powders to CsPbX3 Perovskite Nanowires: One-Pot Synthesis, Growth Mechanism, and Oriented Self-Assembly. Angew. Chem. Int. Ed. 2017, 56, 13887-13892. (28) Pan, Q.; Hu, H.; Zou, Y.; Chen, M.; Wu, L.; Yang, D.; Yuan, X.; Fan, J.; Sun, B.; Zhang, Q. MicrowaveAssisted Synthesis of High-Quality “All-Inorganic” CsPbX3 (X = Cl, Br, I) Perovskite Nanocrystals and Their Application in Light Emitting Diodes. J. Mater. Chem. C 2017, 5, 10947-10954. (29) Zhu, Z.-Y.; Yang, Q.-Q.; Gao, L.-F.; Zhang, L.; Shi, A.-Y.; Sun, C.-L.; Wang, Q.; Zhang, H.-L. Solvent-Free Mechanosynthesis of Composition-Tunable Cesium Lead Halide Perovskite Quantum Dots. J. Phys. Chem. Lett. 2017, 8, 1610-1614. (30) Chen, C.-Y.; Lin, H.-Y.; Chiang, K.-M.; Tsai, W.-L.; Huang, Y.-C.; Tsao, C.-S.; Lin, H.-W. All-VacuumDeposited Stoichiometrically Balanced Inorganic Cesium Lead Halide Perovskite Solar Cells with Stabilized Efficiency Exceeding 11%. Adv. Mater. 2017, 29, 1605290. (31) Tang, Y.; Lu, H.; Rao, L.; Li, Z.; Ding, X.; Yan, C.; Yu, B. Regulating the Emission Spectrum of CsPbBr3 from Green to Blue via Controlling the Temperature and Velocity of Microchannel Reactor. Materials 2018, 11, 371. (32) Pan, A.; He, B.; Fan, X.; Liu, Z.; Urban, J. J.; Alivisatos, A. P.; He, L.; Liu, Y. Insight into the LigandMediated Synthesis of Colloidal CsPbBr3 Perovskite Nanocrystals: The Role of Organic Acid, Base, and Cesium Precursors. ACS Nano 2016, 10, 7943-7954. (33) Jaya, S.; Das, H. Effect of Maltodextrin, Glycerol Monostearate and Tricalcium Phosphate on Vacuum Dried Mango Powder Properties. J. Food Eng. 2004, 63, 125-134. (34) Wang, Y.; Ma, J.-B.; Zhou, Q.; Pang, S.-F.; Zhang, Y.-H. Hygroscopicity of Mixed Glycerol/Mg(NO3)2/Water Droplets Affected by the Interaction between Magnesium Ions and Glycerol Molecules. J. Phys. Chem. B 2015, 119, 5558-5566. (35) Du, X.; Wu, G.; Cheng, J.; Dang, H.; Ma, K.; Zhang, Y.-W.; Tan, P.-F.; Chen, S. High-Quality CsPbBr3 Perovskite Nanocrystals for Quantum Dot Light-Emitting Diodes. RSC Adv. 2017, 7, 10391-10396. (36) Cottingham, P.; Brutchey, R. L. On the Crystal Structure of Colloidally Prepared CsPbBr3 Quantum Dots. Chem. Commun. 2016, 52, 5246-5249. (37) Bertolotti, F.; Protesescu, L.; Kovalenko, M. V.; Yakunin, S.; Cervellino, A.; Billinge, S. J. L.; Terban, M. W.; Pedersen, J. S.; Masciocchi, N.; Guagliardi, A. Coherent Nanotwins and Dynamic Disorder in Cesium Lead Halide Perovskite Nanocrystals. ACS Nano 2017, 11, 3819-3831. (38) Chen, W.; Xin, X.; Zang, Z.; Tang, X.; Li, C.; Hu, W.; Zhou, M.; Du, J. Tunable Photoluminescence of CsPbBr3 Perovskite Quantum Dots for Light Emitting Diodes Application. J. Solid State Chem. 2017, 255, 115-120. (39) Liang, Z.; Zhao, S.; Xu, Z.; Qiao, B.; Song, P.; Gao, D.; Xu, X. Shape-Controlled Synthesis of All-Inorganic CsPbBr3 Perovskite Nanocrystals with Bright Blue Emission. ACS Appl. Mater. Interfaces 2016, 8, 2882428830. (40) Zhang, M.; Zheng, Z.; Fu, Q.; Chen, Z.; He, J.; Zhang, S.; Yan, L.; Hu, Y.; Luo, W. Growth and Characterization of All-Inorganic Lead Halide Perovskite Semiconductor CsPbBr3 Single Crystals. CrystEngComm 2017, 19, 6797-6803. 19 ACS Paragon Plus Environment


(41) Wang, M.; Li, B.; Yuan, J.; Huang, F.; Cao, G.; Tian, J. Repairing Defects of Halide Perovskite Films to Enhance Photovoltaic Performance. ACS Appl. Mater. Interfaces 2018, 10, 37005-37013. (42) Yasutaka, N.; Katie, H. K.; Rui, T.; Ruipeng, L.; Zhongwu, W.; Ou, C. Nanocube Superlattices of Cesium Lead Bromide Perovskites and Pressure-Induced Phase Transformations at Atomic and Mesoscale Levels. Adv. Mater. 2017, 29, 1606666. (43) Akkerman, Q. A.; Motti, S. G.; Srimath Kandada, A. R.; Mosconi, E.; D’Innocenzo, V.; Bertoni, G.; Marras, S.; Kamino, B. A.; Miranda, L.; De Angelis, F., et al. Solution Synthesis Approach to Colloidal Cesium Lead Halide Perovskite Nanoplatelets with Monolayer-Level Thickness Control. JACS 2016, 138, 10101016. (44) Zhao, J.; Cao, S.; Li, Z.; Ma, N. Amino Acid-Mediated Synthesis of CsPbBr3 Perovskite Nanoplatelets with Tunable Thickness and Optical Properties. Chem. Mater. 2018, 30, 6737-6743. (45) Löper, P.; Moon, S.-J.; Martín de Nicolas, S.; Niesen, B.; Ledinsky, M.; Nicolay, S.; Bailat, J.; Yum, J.-H.; De Wolf, S.; Ballif, C. Organic–Inorganic Halide Perovskite/Crystalline Silicon Four-Terminal Tandem Solar Cells. Phys. Chem. Chem. Phys. 2015, 17, 1619-1629. (46) Weidman, M. C.; Goodman, A. J.; Tisdale, W. A. Colloidal Halide Perovskite Nanoplatelets: An Exciting New Class of Semiconductor Nanomaterials. Chem. Mater. 2017, 29, 5019-5030. (47) de Weerd, C.; Gomez, L.; Zhang, H.; Buma, W. J.; Nedelcu, G.; Kovalenko, M. V.; Gregorkiewicz, T. Energy Transfer Between Inorganic Perovskite Nanocrystals. J. Phys. Chem. C 2016, 120, 13310-13315. (48) Wei, Z.; Perumal, A.; Su, R.; Sushant, S.; Xing, J.; Zhang, Q.; Tan, S. T.; Demir, H. V.; Xiong, Q. SolutionProcessed Highly Bright and Durable Cesium Lead Halide Perovskite Light-Emitting Diodes. Nanoscale 2016, 8, 18021-18026. (49) Sadhanala, A.; Ahmad, S.; Zhao, B.; Giesbrecht, N.; Pearce, P. M.; Deschler, F.; Hoye, R. L.; Godel, K. C.; Bein, T.; Docampo, P., et al. Blue-Green Color Tunable Solution Processable Organolead ChlorideBromide Mixed Halide Perovskites for Optoelectronic Applications. Nano Lett. 2015, 15, 6095-6101. (50) Nakamura, S.; Krames, M. R. History of Gallium Nitride-Based Light-Emitting Diodes for Illumination. Proc. IEEE 2013, 101, 2211-2220. (51) Zhu, P.; Tansu, N. Effect of Packing Density and Packing Geometry on Light Extraction of III-Nitride Light-Emitting Diodes with Microsphere Arrays. Photonics Res. 2015, 3, 184-191. (52) Zhu, P.; Tansu, N. Resonant Cavity Effect Optimization of III-Nitride Thin-Film Flip-Chip Light-Emitting Diodes with Microsphere Arrays. Appl. Opt. 2015, 54, 6305-6312. (53) Ooi, Y. K.; Liu, C.; Zhang, J. Analysis of Polarization-Dependent Light Extraction and Effect of Passivation Layer for 230-nm AlGaN Nanowire Light-Emitting Diodes. IEEE Photonics J. 2017, 9, 4501712. (54) Zhu, P.; Zhu, H.; Qin, W.; Dantas, B. H.; Sun, W.; Tan, C.-K.; Tansu, N. Narrow-Linewidth Red-Emission Eu3+-Doped TiO2 Spheres for Light-Emitting Diodes. J. Appl. Phys. 2016, 119, 124305. (55) McKittrick, J.; Shea-Rohwer, L. E.; Green, D. J. Review: Down Conversion Materials for Solid-State Lighting. J. Am. Ceram. Soc. 2014, 97, 1327-1352. (56) Lephoto, M. A.; Tshabalala, K. G.; Motloung, S. J.; Shaat, S. K. K.; Ntwaeaborwa, O. M. Tunable Emission from LiBaBO3:Eu3+;Bi3+ Phosphor for Solid-State Lighting. Luminescence 2017, 32, 1084-1091. (57) Zhu, P.; Wang, W.; Zhu, H.; Vargas, P.; Bont, A. Optical Properties of Eu3+-Doped Y2O3 Nanotubes and Nanosheets Synthesized by Hydrothermal Method. IEEE Photonics J. 2018, 10, 4500210. (58) Pust, P.; Schmidt, P. J.; Schnick, W. A Revolution in Lighting. Nat. Mater. 2015, 14, 454-458.


Page 20 of 21

Page 21 of 21 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


TOC Graphic


Saponification Precipitation Method of CsPbBr3 Nanocrystals with

Recommend Documents