Combination of Hybrid CVD and Cation Exchange for Upscaling Cs-Substituted Mixed Cation Perovskite Solar Cells with High Efficiency and Stability

Mixed cation hybrid perovskites such as Cs_xFA_{1− x}PbI₃ are promising materials for solar cell applications, due to their excellent photoelectronic properties and improved stability. Although power conversion efficiencies (PCEs) as high as 18.16% have been reported, devices are mostly processed by the anti-solvent method, which is difficult for further scaling-up. Here, a method to fabricate Cs_xFA_{1− x}PbI₃ by performing Cs cation exchange on hybrid chemical vapor deposition grown FAPbI₃ with the Cs⁺ ratio adjustable from 0 to 24% is reported. The champion perovskite module based on Cs_0.07FA_0.93PbI₃ with an active area of 12.0 cm² shows a module PCE of 14.6% and PCE loss/area of 0.17% cm⁻², demonstrating the significant advantage of this method toward scaling-up. This in-depth study shows that when the perovskite films prepared by this method contain 6.6% Cs⁺ in bulk and 15.0% at the surface, that is, Cs_0.07FA_0.93PbI₃, solar cell devices show not only significantly increased PCEs but also substantially improved stability, due to favorable energy level alignment with TiO₂ electron transport layer and spiro-MeOTAD hole transport layer, increased grain size, and improved perovskite phase stability.