Effect of energetic distribution of trap states on fill factor in perovskite solar cells

Abstract

Fill factor is a critical parameter for characterizing the performance of perovskite solar cells and is speculated to be closely related to the trap states, while the underlying correlation remains unclear. In this work, the effect of the energetic distribution of trap states in perovskite on the fill factor of the device is systemically investigated. Perovskite films with distinct trap states are prepared with/without the dimethyl sulfoxide additive, based on which the corresponding devices exhibit different power conversion efficiency and fill factors, but similar open-circuit voltages and short-circuit currents. Subsequently, the recombination dynamics process, trapping/detrapping efficiency and transport property of the photo-generated charge carrier are fully studied. Moreover, it is found that the difference in the energetic distribution of trap states leads to the variation of charge recombination/transport dynamics. The energetic distribution of trap states also determines the activation energy of thermal-assisted carrier detrapping and charge collection efficiency, which further affects the FF behavior. The passivation of trap state, especially deep trap states, could reduce the charge recombination loss, make the charge detrapping process more efficient, modify the charge transport property, improve the charge collection efficiency and eventually lead to the enhancement of FF.