Hematite electron-transporting layers for environmentally stable planar perovskite solar cells with enhanced energy conversion and lower hysteresis

Abstract

Non-obvious hysteresis and higher steady-state power conversion efficiency (PCE) were demonstrated by simply employing hematite (α-Fe₂O₃) as the electron transporting layer (ETL) to replace the conventional titania (TiO₂) ETL in planar heterojunction perovskite solar cells. The achieved higher built-in potential across the perovskite layer for the devices using α-Fe₂O₃ ETLs led to more efficient charge extraction/transport and less charge recombination than using TiO₂ ETLs. As a consequence, a significant reduction in the charge accumulation at the perovskite/α-Fe₂O₃ interface made the device much less sensitive to the scanning rate and direction, i.e., lower hysteresis. Furthermore, α-Fe₂O₃ based devices displayed good stability over 30 days of storage time with exposure to ambient air, owing to the higher crystalline quality and uniform grain size of the perovskite films deposited on α-Fe₂O₃ ETLs than on TiO₂ ETLs.