All-Inorganic Perovskite Solar Cells with Tetrabutylammonium Acetate as the Buffer Layer between the SnO2 Electron Transport Film and CsPbI3

All-inorganic CsPbI 3 perovskites have great potential in tandem cells in combination with other photovoltaic devices. However, CsPbI 3 perovskite solar cells (PSCs) still face a huge challenge, resulting in a low power conversion efficiency (PCE) relative to organic–inorganic PSCs. In this work, we introduced tetrabutylammonium acetate (TBAAc) as a buffer layer between the SnO 2 electron-transport layer (ETL) and CsPbI 3 all-inorganic perovskite film interface for the first time. TBAAc not only improved the conductivity of SnO 2 ETL but also formed a 1D TBAPbI 3 layer between the SnO 2 ETL and the 3D CsPbI 3 all-inorganic perovskite film, thereby enhancing the stability and passivating the surface defects of the CsPbI 3 perovskite to fabricate high-efficiency carbon-counter electrode (CE)-based CsPbI 3 solar cells. We fabricated carbon-CE-based hole-transporting layer ( HTL)-free PSCs with an FTO/SnO 2 /TBAAc/CsPbI 3 /C structure. The open-circuit voltage ( V oc ), short circuit current density ( J sc ), PCE, and fill factor of the champion CsPbI 3 PSCs simultaneously enhanced to 1.08 V, 17.48 mA/cm 2, 12.79, and 67.8%, respectively. This PCE is currently one of the high efficiencies reported for the above planar-structured carbon-CE-based CsPbI 3 PSCs to date. Moreover, the optimized device exhibits excellent stability, which retained over 83% of its initial PCE after 350 h. This work provides a facile way of simultaneous optimization of the SnO 2 ETL and the CsPbI 3 perovskite layer to fabricate stable and high-efficiency carbon-CE-based CsPbI 3 PSCs.