A vapor-assisted annealing strategy towards high-quality perovskite absorbers enabling efficient wide bandgap perovskite solar cells

Vapor-deposited wide bandgap (WBG) perovskite solar cells are attracting considerable interest due to their scalability and compatibility with silicon/perovskite monolithic tandem devices. However, producing highquality WBG perovskite thin films through vapor-based techniques is challenging, primarily due to the difficulties in controlling the stoichiometric ratios and achieving uniform distribution of organic and inorganic ions. In this research, we meticulously control the doping levels of Cs and Br during the evaporation of inorganic precursors, resulting in perovskite films with optimal bandgaps for tandem applications. Then, by employing vapor-assisted pressure-controlled annealing (VA-PCA) with a combination of 4-fluorophenylmethylammonium bromide (F-PMABr) and ammonium fluoride (NH4F), we achieve homogeneous, pinhole-free WBG perovskite films of exceptional quality. This method synergistically addresses both surface and bulk defects. The incorporation of small ions and molecules mitigates halide vacancy defects and fortifies the lattice structure, effectively curbing detrimental ion migration and minimizing phase segregation in WBG perovskites. Consequently, the highest power conversion efficiency achieved by our fabricated inverted WBG perovskite solar cell is 20.10 %. Impressively, when encapsulated, the device maintains 82.3 % of its original efficiency after continuous exposure to air and illumination for 456 hours, demonstrating strong potential for applications in silicon/perovskite tandem devices.