Ternary Two‐Step Sequential Deposition Induced Perovskite Orientational Crystallization for High‐Performance Photovoltaic Devices

Abstract State‐of‐the‐art, high‐performance formamidinium‐lead‐iodide‐based (FAPbI 3 ‐based) perovskite photovoltaics are mainly prepared by one‐step antisolvent dripping deposition or two‐step sequential fabrication methods. Compared with the one‐step deposition, the two‐step fabricated perovskite films tend to grow columnar perovskite grains vertically which is easier for carrier extraction and transportation. Herein, the concept of formamidinium methylammonium cesium based ternary‐cation two‐step sequential deposition method is put forward by incorporating cesium acetate (CsAc) into a lead iodide precursor, which generates CsPbI 3 crystal nuclei improving the further perovskite crystallization. When the formamidinium/methylammonium‐based organic amine salts solution is spin coated on the PbI 2 substrate, the acetate moves upward and induces perovskite orientational and uniform crystallization, which can go a step further for the vertical columnar grains achieving fewer defects and higher photovoltaic efficiency. The champion outdoor power conversion efficiency of the modified device under AM 1.5G reaches 21.50% and its indoor efficiency at 1000 lux reaches 40.99%. This work paves the way for further exploring ternary‐cation two‐step sequential deposition methods to prepare high‐performance perovskite photovoltaics.