ROOM TEMPERATURE FACILE SYNTHESES OF LEAD BROMIDE PEROVSKITES

ABSTRACT

In this work, the bright CsPbBr3 and MAPbBr3 perovskites quantum dots quantum dots for solar cells were synthesized at room temperature in this work. The formation of quantum dots was investigated in the received perovskite CsPbBr3 and MAPbBr3. Furthermore, the quantum dots of CsPbBr3 and MAPbBr3 were studied using the electronic absorption and emission spectra.

АННОТАЦИЯ

В данной работе при комнатной температуре были синтезированы яркие квантовые точки перовскитов CsPbBr₃ и MAPbBr₃ — квантовые точки для солнечных элементов. Было исследовано образование квантовых точек в полученных перовскитах CsPbBr₃ и MAPbBr₃. Кроме того, квантовые точки CsPbBr₃ и MAPbBr₃ были изучены с использованием электронных спектров поглощения и эмиссии. 

Keywords: CsPbBr₃, MAPbBr₃, perovskite, quantum dots, synthesis, absorption, emission, antisolvent.

Ключевые слова: CsPbBr₃, MAPbBr₃, перовскит, квантовые точки, синтез, поглощение, эмиссия, антирастворитель.

Introduction.

In the recent past, all inorganic perovskite materials have become the subject of hype due to their high carrier mobility, high radiation recombination efficiency, high color purity, and a variable bandgap; as a consequence, they have become excellent candidates for next-generation light-emitting devices [1-3].

Perovskite materials are generally characterized by the generic formula ABX₃, where the metallic component A is typically a monovalent organic or metal cation such as Cs⁺, MA⁺, or FA⁺, while B is usually a divalent metal cation, mostly Pb⁺², and Sn⁺². The halide anion, X, is typically Cl^-, Br^-, or I^-. The regular octahedral perovskite structure is shown in Figure 1.

Figure 1. The crystal structure of perovskites

Perovskite solar cells were first reported in 2009, proving that the perovskite semiconductor presents room for applications in Nanotechnology. Currently, the power conversion efficiency of the perovskite solar cell has grown to 25.2% in the last years [4,5]. For CsPbX₃ (X = Cl, Br, I) QDs, the most commonly used methods include the hot-injection method, room temperature antisolvent methods, and ion exchange methods. The hot injection method has the advantage of synthesizing high-performance perovskite nanomaterials.

Protesescu et al injected the pre-prepared cesium oleate precursor into dissolved oleic acid OAm, and octadecene ODE under high temperature and nitrogen flow conditions in the PbX₂ solution, and then, the temperature of the reaction was rapidly cooled to room temperature, and the reaction solution was centrifuged to obtain the original perovskite solution. The hot-injection method introduces OA and OAm ligands, which provides the possibility for the subsequent study of ligand modification and makes it possible to introduce ions into the perovskite lattice. Since the perovskite QDs materials are essentially ionic crystals, ion migration can take place in the solution.

Since perovskite QDs materials are ionic gems, particle relocation can take put within the arrangement. By including diverse halogen components to the perovskite QDs arrangement arranged by warm infusion and other strategies, perovskite QDs with distinctive photoluminescence wavelength ranges can be arranged. Nedelcu et al. accomplished the preparation of perovskite QDs within the whole obvious light locale by halfway or full anion trade at room temperature [7]. Be that as it may, blending diverse incandescent lamps will lead to the stage partition of QDs causing to decrease in photostability. 

The main difference in solubility between materials in different solvents is mainly due to the principle that solubility is completely different in different solutions. The room temperature method uses PbX₂ and CsX as material sources dissolves them in DMF (i.e. Dimethylformamide) and then injects them into the solution of toluene. The solvent is highly supersaturated and a large number of crystals precipitate from the solution. However, this method still needs OA (or OAm) as a surface ligand for the passivation of surface defects and to improve the stability of the QDs material. Since the entire experimental process is performed at room temperature the preparation process is very straightforward and inexpensive. However, the uniformity of QDs obtained in this way is not very appealing [9].

Schmide et al., [10] coined the term LARP (Ligand-Assisted Reprecipitation) to describe the process of preparing MAPbX₃ perovskite QDs using a facile colloid strategy. They used ligands with medium-sized chains to stabilize the colloid phase. Li et al., [11], also used ligand assistance to prepare inorganic perovskites (PPs) at room temperature. Yang et al., [12], used a different approach. First, they dissolved CsBr into deionized water. Then, they dissolved PbBr₂ into DMF. Finally, they mixed Oleic acid and N-Oxylamine in 10 ml hexane. In a normal process, they made the ‘oil phase’ by mixing oleic acid with n-octylamine in 10 mL hexane. Then, the oil phase was dropwise precipitated with a solution of CsBr · H₂O + PbBr₂ · DMF. The oil phase gradually changed from a clear to a pale white color, and an emulsion was formed. Acetone was then used to initiate the deemulsion process. The QDs were precipitated after centrifugation of the mixture. The mechanisms behind LARP vs. emulsion are similar, but the supersaturated environments differ. In LARP, the solvent is mixed in such a way that it changes the solubility of the solvent and nucleates the QDs. On the other hand, in emulsion methods, the solubility is changed by the microreactors resulting from solvent mixing.

Experimental part.

The following reagents were used for the synthesis of perovskites: Lead (II) bromide (PbBr₂ 99.99%); Cesium bromide (CsBr 99.99%); methylammonium bromide (MABr); octylammonium bromide (OAmBr); dimethylformamide (DMF); dimethylsulfoxide (DMSO); oleylamine (C₁₈H₃₆NH₂); oleic acid (C₁₇H₃₃COOH); toluene (as an antisolvent); chloroform. All reagents have been analytically graded and have not been subjected to any further purification.

 The MAPbBr₃ and CsPbBr₃ perovskite formation process can be described as follows:

CsBr + PbBr₂ → CsPbBr₃ (in DMSO)

MABr + PbBr₂ → MAPbBr₃ (in DMF)

Synthesis of CsPbBr₃. The following procedure was used to create perovskite material quantum dots: The salts CsBr and PbBr2 were measured in the proper mass at a 1:1 mol ratio. The solvent that was employed was dimethylsulfoxide (DMSO). For twelve hours, 0.1M solutions of CsBr and PbBr₂ in DMSO were agitated at room temperature using a magnetic stirrer. These precursors were then combined in a single container with 1 ml. The CsBr + PbBr₂ solution was supplemented with 0.1 ml of oleinamine (OAm) and 0.2 ml of oleic acid (OA) as ligands. There was no precipitation during the synthesis since the salts were all dissolved in the solvents. Using a magnetic stirrer, 0.1 ml of the produced perovskite (CsPbBr₃) solution was combined with 6 ml of toluene solution. A brilliant green CsPbBr₃ perovskite quantum dot (0.000416M) was the end product. The LARP approach was used to conduct this experiment.

Synthesis of MAPbBr₃. Using an analytical balance with a 1:1 mol ratio, the appropriate mass of MABr and PbBr₂ salts were measured. As a solvent, 5 milliliters of dimethylformamide (DMF) were utilized. To get the salts to dissolve completely, it was heated and agitated for a long period. The resultant 0.02M MABr + PbBr₂ solution was added to with 0.1 ml of oleinamine (OAm), 0.2 ml of oleic acid (OA), and 0.0001 g of octylammonium bromide (C8H20BrN) as a ligand. Using a magnetic stirrer, 0.1 ml of the resultant ligand solution was combined with 10 ml of chloroform (an antisolvent). Consequently, a vivid blue (10^-6 M) MAPbBr3 perovskite quantum dot was seen to form. The previously stated LARP approach was also used to complete this synthesis.

The perovskite quantum dot samples that are produced by both techniques had their spectra examined and utilized in further experiments.

Results and discussion.

A spectrophotometer (UV-2600i, Shimadzu, Japan) and a spectrofluorimeter (RF-6000, Shimadzu, Japan) were used to measure the spectra of the solutions of brilliant perovskite (CsPbBr3) and (MAPbBr3) quantum dots.

Fig. 2 shows that the fabricated CsPbBr3 perovskite has an absorption maximum of around 518 nm. In other words, spectrum research revealed that this quantum dot has a spectrum in the green region.

Figure 2. Fluorescence emission spectrum of CsPbBr₃ perovskite quantum dots

The synthesis of MAPbBr₃ perovskite involves the inclusion of octylammonium bromide (C₈H₂₀BrN) as a ligand, together with oleic acid and oleic amine. Toluene and chloroform are used as antisolvents, and this allows us to identify the spectrum of the solution of this perovskite quantum dot in the bright blue region (Fig. 3).

The emission spectra of the yielded MAPbBr₃ perovskite quantum dots with various antisolvents can be viewed in Figure 3. The peak absorption of MAPbBr₃ perovskite may be observed at 457 nm in the case of chloroform antisolvent and 453 nm in the case of toluene antisolvent. Therefore, it is evident that the vibrant blue part of the perovskite quantum dot solution's spectrum is created when octylammonium bromide is added as a ligand during the production process at ambient temperature. Spectral analysis was used to determine these observations.

In the MAPbBr₃ synthesis, perovskite quantum dots with an apparent green emission were formed when oleic acid and oleic amine were utilized as ligands. Nevertheless, the hue turned blue when ligands such as oleic acid, oleic amine, and octylammonium bromide were added.  Furthermore, it was discovered that the formation of quantum dots is impacted by the antisolvents used, which vary in composition. The spectrum of quantum dots produced by various antisolvent combinations is displayed in Figure 3.

Figure 3. Fluorescence emission spectra of MAPbBr₃ perovskite quantum dots in toluene and chloroform

When chloroform is used as an antisolvent, as can be observed in Fig. 4 above, intense blue perovskite quantum dots are formed. Using toluene as an antisolvent causes the creation of brilliant blue perovskite quantum dots, as seen in Fig. 5. The LARP technique was used to create both perovskites at room temperature.

Conclusions.

At routine temperatures, fluorescent blue MAPbBr₃ and bright green CsPbBr₃ perovskite quantum dots were produced. Following spectroscopic analysis, the produced perovskite compounds showed evidence of a formation of blue and green quantum dots. The occurrence of the absorption maximum of perovskite quantum dots in the bright blue region was observed to be caused by the use of octylammonium bromide as a ligand during the production of MAPbBr3, in addition to oleic acid and oleic amine.

References:

1. Akkerman, Q. A., Rainò, G., Kovalenko, M. V., and Manna, L. (2018). Genesis, Challenges, and Opportunities for Colloidal Lead Halide Perovskite Nanocrystals. Nat. Mater 17 (5), 394–405. doi:10.1038/s41563-018-0018-4
2. Fu, Y., Zhu, H., Chen, J., Hautzinger, M. P., Zhu, X.-Y., and Jin, S. (2019). Metal Halide Perovskite Nanostructures for Optoelectronic Applications and the Study of Physical Properties. Nat. Rev. Mater. 4 (3), 169–188. doi:10.1038/s41578-019-0080-9
3. Xu, J., Zhang, H., Wu, C., and Dai, J. (2020a). Stable CsPbX₃@SiO₂ Perovskite Quantum Dots for White-Light Emitting Diodes. J. Nanoelectron. Optoelectron.15 (5), 599–606. doi:10.1166/jno.2020.2824
4. Kojima, A., Teshima, K., Shirai, Y., and Miyasaka, T. (2009). Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc.131 (17), 6050–6051. doi:10.1021/ja809598r
5. Roy, P., Kumar Sinha, N., Tiwari, S., and Khare, A. (2020). A Review on Perovskite Solar Cells: Evolution of Architecture, Fabrication Techniques, Commercialization Issues and Status. Solar Energy 198, 665–688. doi:10.1016/j.solener.2020.01.080
6. Protesescu, L., Yakunin, S., Bodnarchuk, M. I., Krieg, F., Caputo, R., Hendon, C. H., et al. (2015). Nanocrystals of Cesium Lead Halide Perovskites (CsPbX₃, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut. Nano Lett. 15 (6), 3692–3696. doi:10.1021/nl5048779
7. Nedelcu, G., Protesescu, L., Yakunin, S., Bodnarchuk, M. I., Grotevent, M. J., and Kovalenko, M. V. (2015). Fast Anion-Exchange in Highly Luminescent Nanocrystals of Cesium Lead Halide Perovskites (CsPbX₃, X = Cl, Br, I). Nano Lett. 15 (8), 5635–5640. doi:10.1021/acs.nanolett.5b02404
8. Pan, J., Quan, L. N., Zhao, Y., Peng, W., Murali, B., Sarmah, S. P., et al. (2016). Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering. Adv. Mater. 28 (39), 8718–8725. doi:10.1002/adma.201600784
9. Yuejia Wu, Ruijun Jia , Jian Xu, Lei Song, Yuxin Liu , Yuman Zhang, Shahid Ullah1 and Jun Dai (2022). Strategies of Improving CsPbX₃ Perovskite Quantum Dots Optical Performance. Frontiers in Materials. doi: 10.3389/fmats.2022.845977
10. L.C. Schmidt, A. Pertegas, S. Gonzalez-Carrero, O.Malinkiewicz, S. Agouram, et al., Nontemplate synthesis ofCH3NH3PbBr3 perovskite nanoparticles. J. Am. Chem. Soc.136, 850–853 (2014). https:// doi. org/ 10. 1021/ ja410 9209
11. F. Zhang, H. Zhong, C. Chen, X. Wu, X. Hu et al., Bright luminescent and color-tunable colloidal CH₃NH₃PbX₃(X=Br, I, Cl) quantum dots: potential alternatives for display technology. ACS Nano 9(4), 4533–4542 (2015). https:// doi.org/ 10. 1021/ acsna no. 5b011 54 
12. X. Li, Y. Wu, S. Zhang, B. Cai, Y. Gu et al., CsPbX₃ quantum dots for lighting and displays: room-temperature synthesis, photoluminescence superiorities, underlying origin sand white light-emitting diodes. Adv. Funct. Mater. 26(15),2435–2445 (2016). https:// doi. org/ 10. 1002/ adfm. 20160 0109
13. W. Yang, R. Su, D. Luo, Q. Hu, F. Zhang, et al., Surface modification induced by perovskite quantum dots for triplication perovskite solar cells. Nano Energy 67, 104189 (2020).https:// doi. org/ 10. 1016/j. nanoen. 2019. 104189
14. Chien‑Yu Huang, Hanchen Li, Ye Wu, Chun‑Ho Lin, Xinwei Guan, Long Hu, Jiyun Kim, Xiaoming Zhu1, Haibo Zeng, Tom Wu. Inorganic Halide Perovskite Quantum Dots: A Versatile Nanomaterial Platform for Electronic Applications. Nano-micro letters, https://doi.org/10.1007/s40820-022-00983-6.