Anion Exchange Promoting Non-Impurities Enables Conformable and Efficient Inverted Perovskite Solar Cells

The two-step sequential deposition is promising for control of the crystallization and growth of compact perovskite by separating the deposition of PbI2 and organic salt. Furthermore, thermal evaporated-PbI2 has the potential for textured surfaces. However, the performance of inverted perovskite solar cells by the two-step sequential deposition lags far behind the counterpart fabricated by the one-step deposition from a precursor solution. Here, we found insight into anion exchange in the sequential thermal evaporation-solution process for high-quality perovskite films. The exchange process promotes mass transport and penetration of organic compounds into evaporated PbI2, optimizes phase purity, and enables a homogeneous halide distribution with inhibited phase segregation. The devices fabricated by evaporated-PbI2 as the bottom layer following the solid-solution interdiffusion process yield a champion efficiency of 24.43% (certified 24.18%), which is the highest inverted perovskite solar cells based on evaporated PbI2. Incorporating the scalable blading process for solid-solution interdiffusion, the device exhibits an efficiency up to 22.22%. The resulting conformable and scalable cells maintain 95% of the initial efficiency after operation for 682 h under one sun illumination. This anion-exchange strategy provides instructive significance for future large-area and monolithic perovskite-silicon tandem cells.