Interfacial Engineering and Defect Passivation for Highly Efficient Carbon‐Based Perovskite Solar Cells

The interface regulation between SnO 2 and perovskite is a critical and challenging issue for highly efficient and stable perovskite solar cells (PSCs). Herein, guanidinium sulfate (GA 2 SO 4 ) is introduced as an interface layer between SnO 2 and perovskite, where the ammonium cation in GA 2 SO 4 can provide more hydrogen bonds for strong coordination with surrounding halides, especially uncoordinated I − , while the sulfate ions (SO 4 2− ) are strongly coordinated to Sn 4+ and uncoordinated Pb 2+ , passivating the defects from both the SnO 2 and perovskite layers. With the GA 2 SO 4 ‐modification, hole‐selective layer ‐free carbon‐electrode‐based PSCs (C‐PSCs) are fabricated and exhibited a higher power conversion efficiency of 17.91%, followed by enhanced environmental stability.