Effect of polarization on performance of inverted solar cells based on molecular ferroelectric Hexane-1,6-diammonium pentaiodobismuth without electron transport layer

•A inverted without ETL solar cells using HDA-BiI5 was fabricated.•Effect of multiple polarization on photoelectronic performance of device is revealed.•The reason why the device performance is improved after polarization is discussed. Ferroelectric photovoltaic materials are more stable compared to perovskite materials and are increasingly promising as light absorbing layers for the fabrication of solar cells. In this paper, a narrow bandgap molecular ferroelectric Hexane-1,6-diammonium pentaiodobismuth (HDA-BiI5) is used to fabricate solar cells, and the structure of inverted electron transport-free layer is determined after calculating its conduction band bottom and valence band top. The results show that the short-circuit current density (Jsc) of the device reaches 1.057 mA/cm2 at the third bias scan, which is about 9 times the initial performance of the device. Although the change of open circuit voltage (Voc) is not obvious, while the photoelectric conversion efficiency of the device is improved significantly. The improved photovoltaic performance of the device is due to the combined effect of the depolarization field formed after multiple polarizations and the built-in electric field at the P-N junction.