Synergistic Dual‐Interface Modification and Crystallization Regulation for Efficient and Stable Inorganic Perovskite Solar Cells Based on Carbon Electrode

All inorganic CsPbI 3 perovskite solar cells based on carbon electrodes (C‐IPSCs) possess advantages of high stability and low cost, demonstrating great potential for commercial applications. However, the poor crystallinity of inorganic perovskite films and the interface defects induce massive nonradiative recombination, which limits the improvement of device efficiency and stability. Herein, a multifunctional small molecule, 3‐methylthio‐1‐propylammonium chloride (3MTPACl), is employed to simultaneously improve the crystallinity of inorganic perovskite films and passivate interface defects inside CsPbI 3 C‐IPSCs. It is demonstrated that the S and ammonium (NH 3 + ) of 3MTPACl can coordinate with uncoordinated Pb 2+ on the surface of CsPbI 3 films, passivate surface defects, and improve the energy level arrangement at the interface between CsPbI 3 /carbon electrode. Meanwhile, Cl − ions diffuse throughout the perovskite film from the top to the bottom and accumulate at both the upper and lower interfaces of the CsPbI 3 layer, promoting the formation of CsPbI 3 films with enlarged grain size and enhanced crystallinity. Consequently, defects at the TiO 2 /perovskite interface are effectively passivated, thereby facilitating electron extraction. Therefore, synergistic dual‐interface modification and crystallization regulation are achieved by 3MTPACl posttreatment, which greatly boosts the efficiency of CsPbI 3 C‐IPSC up to 17.61%, accompanied by enhanced humidity, thermal, and long‐term stability.