First-Day Degradation and Night-Time Recovery Mechanisms of Lead-Tin Perovskite Solar Cells

The low bandgap of mixed lead-tin perovskites makes them promising candidates for multijunction perovskite solar cells. However, their inferior stability limits their potential. Here, we study the degradation of devices during the first day of operation. We continuously illuminate devices with either poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) or (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz) hole-transport layers for 12 h at open or short circuit and track their performance using current-voltage and impedance measurements. We subsequently track the recovery of the devices in the dark. We find a permanent burn-in degradation, and multiple ionic processes. Under both aging conditions, ionic field screening decreases the current in both types of devices. After aging at open circuit, the performance fully recovers in the dark, but after aging at short circuit, we observe more permanent degradation and further decrease of the performance in the dark, which we ascribe to trap formation caused by prolonged ion accumulation at the interfaces.