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(x)FA(1-x)PbI(3) 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(x)FA(1-x)PbI(3) by performing Cs cation exchange on hybrid chemical vapor deposition grown FAPbI(3) with the Cs+ ratio adjustable from 0 to 24% is reported. The champion perovskite module based on Cs(0.07)FA(0.93)PbI(3) with an active area of 12.0 cm(2) 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(0.07)FA(0.93)PbI(3), 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.