Surface Passivation of CsPbI (3) Films for Efficient and Stable Hole-Transporting Layer-Free Carbon-Based Perovskite Solar Cells

Hole-transporting layer (HTL)-free CsPbI3 carbon-based perovskite solar cells (C-PSCs) are regarded as a promising photovoltaic candidate due to their low cost and enhanced device stability. However, the imperfect perovskite/carbon interface, including surface defects of CsPbI3 films, unmatched energy level alignment, etc., leads to a low power conversion efficiency (PCE) and thus hampers its further development for commercialization. Herein, a multifunctional interface modifier octylammonium iodide (OAI) is introduced into the CsPbI3/carbon interface, which can not only reduce the amount of residual PbI2 at grain boundaries by converting PbI2 to the (OA)(2)PbI4 two-dimensional (2D) phase but also passivate defects located at the surface and grain boundaries of CsPbI3 films. Consequently, greatly reduced defect density of CsPbI3 films as well as matched energy level alignment of the CsPbI3/carbon interface are achieved, which significantly boost the PCE of CsPbI3 C-PSCs from 12.97 to 14.64%. Moreover, due to the reduced amount of PbI2 at grain boundaries and the hydrophobic property of long-chain alkyl in OAI, the unencapsulated CsPbI3 C-PSCs demonstrate excellent long-term ambient stability, which can retain 91% of its initial PCE after 30 days of storage in air.