Restructuring and Reshaping of CsPbX₃ Perovskites by Lithium Salts

Abstract Metal halide perovskites have exceptional potential for future generations of light‐emitting diodes and solar cells. Compared to widely used solution‐based syntheses, vapor‐phase deposition (VPD) offers a fabrication route that can be more easily scaled up for commercial production. Cesium lead halides (CsPbX₃) have shown great color purity, high photoluminescence quantum yield, and better stability than other perovskites. To improve the optoelectronic properties, lithium salts are often used as passivation agents to reduce nonradiative defects. Here, it is reported that VPD CsPbX₃ thin films can be dramatically reshaped by a lithium bromide adlayer, a salt that is successfully used to drastically increase the luminescent yield of CsPbBr₃. It is found that continuous CsPbBr₃ and CsPbCl₃ films restructure themselves into islands whereas CsPbI₃ films transform into mixed triangular and rod‐shaped crystals. Based on density functional theory (DFT) studies, it is established that a surface energy change by LiBr adlayer is not the main driver for the perovskite film transformation. Instead, DFT simulations indicate that the LiBr adlayer creates a polar surface forming a strong Van der Waals force attracting water molecules.