Controlled Crystal Growth of All-Inorganic CsPbI 2 Br via Sequential Vacuum Deposition for Efficient Perovskite Solar Cells.

Vacuum deposition of perovskites is a promising method for scale-up fabrication and uniform film growth. However, improvements in the photovoltaic performance of perovskites are limited by the fabrication of perovskite films, which are not optimized for high device efficiency in the vacuum evaporation process. Herein, we fabricate CsPbI 2 Br perovskite with high crystallinity and larger grain size by controlling the deposition sequence between PbI 2 and CsBr. The nucleation barrier for perovskite formation is significantly lowered by first evaporating CsBr and then PbI 2 (CsBr-PbI 2 ), followed by the sequential evaporation of multiple layers. The results show that the reduced Gibbs free energy of CsBr-PbI 2 , compared with that of PbI 2 -CsBr, accelerates perovskite formation, resulting in larger grain size and reduced defect density. Furthermore, surface-modified homojunction perovskites are fabricated to efficiently extract charge carriers and enhance the efficiency of perovskite solar cells (PeSCs) by modulating the final PbI 2 thickness before thermal annealing. Using these strategies, the best PeSC exhibits a power conversion efficiency of 13.41% for a small area (0.135 cm 2 ), the highest value among sequential thermal deposition inorganic PeSCs, and 11.10% for a large area PeSC (1 cm 2 ). This study presents an effective way to understand the crystal growth of thermally deposited perovskites and improve their performance in optoelectronic devices.