Cs-substituted mixed cation hybrid perovskites are promising materials for solar cell applications, due to their excellent photo-electronic properties and improved stability. Although power conversion efficiencies (PCEs) as high as 21.1% have been reported, devices are mostly processed by spin coating (e.g., the anti-solvent method) with an active area of < 0.3 cm2, which is difficult for further scaling-up. Here we report a scable method to fabricate Cs-substituted perovskite i.e., CsxFA1-xPbI3 by performing Cs cation exchange on hybrid CVD grown FAPbI3. The perovskite film shows high uniformity over a large area of 10 cm × 10 cm. The champion perovskite module (5 cm × 5 cm) based on Cs0.07FA0.93PbI3 with an active area of 12.0 cm2 shows a module PCE of 14.6% and PCE loss/area of 0.17%/cm2, demonstrating the significant advantage of this method toward scaling-up. Our in-depth study shows that when the perovskite films contain 6.6% Cs+ in bulk, i.e., Cs0.07FA0.93PbI3, 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.
 Y. Jiang, M. R. Leyden, L. Qiu, S. Wang, L. K. Ono, Z. Wu, E. J. Juarez-Perez, Y. B. Qi*, Adv. Funct. Mater. 2017, accepted.