Simultaneous Incorporation of CsI in the Two‐step Deposition Process Boosts the Power Conversion Efficiency and Stability of Perovskite Solar Cells

Abstract Two‐step deposition method has been widely exploited to fabricate FA 1‐x Cs x PbI 3 perovskite solar cells. However, in previous studies, CsI is mainly added into the PbI 2 precursor with DMF/DMSO as solvent. Here in this study, a novel method to fabricate FA 1‐x Cs x PbI 3 perovskite has been proposed. The CsI is simultaneously added into the PbI 2 precursor and the organic FAI/MACl salts solution in our modified two‐step deposition process. The resulting FA 1‐x Cs x PbI 3 film exhibits larger perovskite crystals and suppressed defect density (4.05×10 15 cm −3 ) compared with the reference perovskite film (9.23×10 15 cm −3 ) without CsI. Therefore, the obtained FA 1‐x Cs x PbI 3 perovskite solar cells have demonstrated superior power conversion efficiencies (PCE=21.96 %) together with better long‐term device stability.