Very Small Inverted Hysteresis in Vacuum-Deposited Mixed Organic-Inorganic Hybrid Perovskite Solar Cells

Perovskite solar cells (PSCs) have attracted great interest over the past few years due to their outstanding power conversion efficiencies. However, operational stability still needs to be improved for broad commercial application. A commonly observed phenomenon for PSCs is hysteresis in their current-voltage characteristics, which has been suggested to be related to issues with long-term stability. A thorough understanding of the processes involved in hysteresis may also guide the way to further improving the cells' efficiencies. We fabricate planar p-i-n organic-inorganic hybrid PSCs using three different organic transport layer architectures by vacuum deposition and measured their hysteresis and long-term stability behavior. Our results show that vacuum-deposited PSCs show much weaker hysteresis than in previous studies, where many types of PSCs were involved. For our devices, we also report an inverted hysteresis, where efficiency is somewhat higher for a voltage sweep from short circuit to forward-bias conditions than for the reverse sweep at lower scan rates, which has not commonly been observed in previous studies of PSCs. Finally, we observe that up to 94% of the initial power conversion efficiency of the encapsulated devices remained after storage in the dark for two months.