25.71%‐Efficiency FACsPbI3 Perovskite Solar Cells Enabled by A Thiourea‐based Isomer

Various isomers have been developed to regulate the morphology and reduce defects in state‐of‐the‐art perovskite solar cells. To insight the structure‐function‐effect correlations for the isomerization of thiourea derivatives on the performance of the perovskite solar cells (PSCs), we developed two thiourea derivatives [(3,5‐dichlorophenyl)amino]thiourea (AT) and N‐(3,5‐dichlorophenyl)hydrazinecarbothioamide (HB). Supported by experimental and calculated results, it was found that AT can bind with undercoordinated Pb2+ defect through synergistic interaction between N1 and C=S group with a defect formation energy of 1.818 eV, which is much higher than that from the synergistic interaction between two ‐NH‐ groups in HB and perovskite (1.015 eV). Moreover, the stronger interaction between AT and Pb2+ regulates the crystallization process of perovskite film to obtain a high‐quality perovskite film with high crystallinity, large grain size, and low defect density. Consequently, the AT‐treated FACsPbI3 device engenders an efficiency of 25.71% (certified as 24.66%), which is greatly higher than control (23.74%) and HB‐treated FACsPbI3 devices (25.05%). The resultant device exhibits a remarkable stability for maintaining 91.0% and 95.2% of its initial efficiency after aging 2000 h in air condition or tracking at maximum power point for 1000 h, respectively.