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

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 CsPbI3 crystal nuclei improving the further perovskite crystallization. When the formamidinium/methylammonium-based organic amine salts solution is spin coated on the PbI2 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.