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

The interface regulation between SnO2 and perovskite is a critical and challenging issue for highly efficient and stable perovskite solar cells (PSCs). Herein, guanidinium sulfate (GA2SO4) is introduced as an interface layer between SnO2 and perovskite, where the ammonium cation in GA2SO4 can provide more hydrogen bonds for strong coordination with surrounding halides, especially uncoordinated I−, while the sulfate ions (SO42−) are strongly coordinated to Sn4+ and uncoordinated Pb2+, passivating the defects from both the SnO2 and perovskite layers. With the GA2SO4‐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.