25.24%‐Efficiency FACsPbI3 Perovskite Solar Cells Enabled by Intermolecular Esterification Reaction of DL‐Carnitine Hydrochloride

Abstract Judicious tailoring of the interface between the SnO 2 electron‐transport layer and the perovskite buried surface plays a pivotal role in obtaining highly efficient and stable perovskite solar cells (PSCs). Herein, a DL‐carnitine hydrochloride (DL) is incorporated into the perovskite/SnO 2 interface to suppress the defect‐states density. A DL‐dimer is obtained at the interface by an intermolecular esterification reaction. For the SnO 2 film, the Cl − in the DL‐dimer can passivate oxygen vacancies (V O ) through electrostatic coupling, while the N in the DL‐dimer can coordinate with the Sn 4+ to passivate Sn‐related defects. For the perovskite film, the DL‐dimer can passivate FA + defects via hydrogen bonding and Pb‐related defects more efficiently than the DL monomer. Upon DL‐dimer modification, the interfacial defects are effectively passivated and the quality of the resultant perovskite film is improved. As a result, the DL‐treated device achieves a gratifying open‐circuit voltage ( V OC ) of 1.20 V and a champion power conversion efficiency (PCE) of 25.24%, which is a record value among all the reported FACsPbI 3 PSCs to date. In addition, the unencapsulated devices exhibit a charming stability, sustaining 99.20% and 90.00% of their initial PCEs after aging in air for 1200 h and continuously operating at the maximum power point tracking for 500 h, respectively.