Interfacing pristine BiI3 onto TiO2 for efficient and stable planar perovskite solar cells

Organic-inorganic lead halide perovskite soalr cells (PSCs) are emerging as one of the most promising photovoltaic technologies owing to their excellent performance and low-cost fabrication process. However, their further practical applications are still limited by the poor long-term stability. Here, we demonstrate that both of the photovoltaic conversion efficiency (PCE) and stability of the solar cells are greatly promoted by employing BiI3 as an interface modifier on the compact TiO2 (c-TiO2) electron transport layer (ETL) in planar PSCs. The crystalline quality and surface morphology of perovskite films are greatly improved by applying the BiI3 layer. The efficiency of electron extraction from the perovskite/ETL interface is also greatly improved. The average PCE of planar PSC solar cells is increased from 13.85 to 16.15% by introducing the BiI3 layer, and a highest PCE of 17.79% is realized. The optimal solar cell also show remarkably higher long-term stability under ambient conditions and strongly positive impact upon the suppression of hysteresis than the pristine devices without BiI3 layer. The present work provides an effectual way to improve both of the efficiency and stability of perovskite-based optoelectronic devices.