Role of Capped Oleyl Amine in the Moisture‐Induced Structural Transformation of CsPbBr₃ Perovskite Nanocrystals

Abstract

The moisture‐induced structural decomposition of lead halide perovskites is the major challenge in solar cells and light‐emitting diodes based on perovskites as the active material. The presence of moisture results in the structural conversion of cubic 3D CsPbBr3 nanocrystals to 2D CsPb2Br5 nanosheets before its decomposition to PbBr2. The capping agent used, oleyl amine, plays a crucial role in this structural transformation. The presence of moisture converts the capping agent, oleyl amine, to its salt, which transforms the 3D CsPbBr3 perovskite nanocrystals to 2D CsPb2Br5 nanosheets. Further, these CsPb2Br5 nanosheets decompose to trigonal PbBr2, in the presence of higher amounts of water. Also, the amount of capping agent, oleyl amine, plays an important role in the rate of moisture‐induced structural transformations. The rate of decomposition increases with the amount of oleyl amine used as a result of the reaction of water with the excess ligands. By revealing the exact mechanism of the structural alterations in the presence of water, new design strategies can be used to prevent the decomposition of perovskites.

Low‐Dimensional‐Networked Cesium Lead Halide Perovskites: Properties, Fabrication, and Applications

“…Considering the ultrahigh solubility of CsX in polar solvents such as water, the water-triggered transformation CsPbX 3 →CsPb 2 X 5 by CsX stripping was widely investigated, and has been the most commonly used strategy in this conversion. [72,149,[161][162][163][164] In Bakr's work, [72] water could be employed to directly transform CsPbBr 3 films to highly luminescent and stable CsPb 2 Br 5 films. At the initial step, water accelerated the extraction of CsBr from CsPbBr 3 , because of the high solubility of CsBr in water and the ionic nature of CsPbBr 3 .…”

Anion Exchange in Lead Halide Perovskites: An Overview

“…[ 27 ] Even though the lead halide perovskites are known to decompose in presence of water, the much fast anion exchange reactions enabled the detection of halide ions in water samples. [ 27,50 ] Moreover, it is very easy to coat lead halide perovskites to any substrates. [ 27 ] For field applications, the solution state detection is hard to perform, and hence sensing with solid substrates is preferred.…”

CsPbBr3 Perovskite–Coated Paper Substrate for the Cost‐Effective Detection of Fluoride, Chloride, and Iodide Ions in Water

“…The diffraction patterns of CsPbBr 3 perovskite nanocrystals match with those of the Joint Committee for Powder Diffraction Standards (JCPDS) and the known values in the literature. [ 39 ] XRD patterns present at 2 θ = 15.4° and 31.08° correspond to (100) and (200) planes of cubic CsPbBr 3 perovskites, respectively. [ 40 ] However, there are small amounts of orthorombic CsPbBr 3 perovskites too.…”

“…The decomposed product shows all the characteristic features of PbBr 2 (Supporting Information). [ 39,43 ] Thus, we used this technique to detect fluoride ions. A schematic representation of the anion exchange reactions of CsPbBr 3 perovskite nanocrystals in the presence of Cl − , F − , and I − is shown in Figure 2E.…”

“…Perovskites are known to decompose in the presence of water. [ 39 ] The water‐induced decomposition is slow in comparison with the anion exchange reaction. [ 39,44–47 ]…”