New Insights into Interfacial Passivation on 3D Graphene–CuInS₂ Composites-Based Perovskite Solar Cells

Although it is generally accepted by the perovskite solar cells community that their interface behaviors have a profound impact on their power conversion efficiency (PCE) and stability, such interfacial engineering on the bottom interface between electron transport layer (ETL) and perovskite film is still lagging. Herein, a 3D graphene (G)–CuInS₂ composite is designed as an efficient ETL to improve both the interfacial contact and passivate defects at the G–CuInS₂/perovskite interface. The lattice matching of graphene and methylammonium lead iodide CH₃NH₃PbI₃ inhibits the concentrated stress generated during the growth of perovskite, resulting in crystal films with large grain boundaries. The low-electron defect density in 3D G–CuInS₂ composite facilitates the electron transport from perovskite film to CuInS₂ quantum dots. In addition, 3D G–CuInS₂ shows excellent carrier extraction capability of reducing carrier extraction time by 1.47 times than that of the counterpart. Correspondingly, a highly improved PCE of 22.4% is obtained, which increases by 15% of the counterpart. Furthermore, the unencapsulated device based on 3D G–CuInS₂ shows long-term stability, maintaining 85% of its original efficiency in air for 30 days. This strategy provides a new route to interfacial passivation engineering for preparation of high-performance perovskite solar cells.