Ni-doped α-Fe2O3 as electron transporting material for planar heterojunction perovskite solar cells with improved efficiency, reduced hysteresis and ultraviolet stability

Abstract

We report on high-efficiency planar heterojunction perovskite solar cells (PSCs) employing Ni-doped α-Fe2O3 as electron-transporting layer (ETL). The suitable addition of nickel (Ni) dopant could enhance the electron conductivity as well as induce downward shift of the conduction band minimum for α-Fe2O3, which facilitate electrons injection and transfer from the conduction band of the perovskite. As a consequence, a substantial reduction in the charge accumulation at the perovskite/ETL interface makes the device much less sensitive to scanning rate and direction, i.e., lower hysteresis. With a reverse scan for the optimized PSC under standard AM-1.5 sunlight illumination, it generates a competitive power conversion efficiency (PCE) of 14.2% with a large short circuit current (Jsc) of 22.35mA/cm2, an open circuit photovoltage (Voc) of 0.92V and a fill factor (FF) of 69.1%. Due to the small J-V hysteresis behavior, a higher stabilized PCE up to 11.6% near the maximum power point can be reached for the device fabricated with 4mol% Ni-doped α-Fe2O3 ETL compared with the undoped α-Fe2O3 based cell (9.2%). Furthermore, a good stability of devices with exposure to ambient air and high levels of ultraviolet (UV)-light can be achieved. Overall, our results demonstrate that the simple solution-processed Ni-doped α-Fe2O3 can be a good candidate of the n-type collection layer for commercialization of PSCs.