Universal Current Losses in Perovskite Solar Cells Due to Mobile Ions

We investigated the origin of current losses in perovskite solar cells, using a combination of voltage dependent photoluminescence (PL) timeseries and various charge extraction measurements. It was demonstrated that Pb/Sn-perovskite devices suffer from a reduction in the charge extraction efficiency within the first few seconds of operation, which leads to a loss in current and lower maximum power output. In addition, the emitted PL from the device rises on the exact same timescales due to the accumulation of electronic charges in the active layer. Using transient charge extraction measurements, we showed that these observations cannot be explained by doping-induced electronic charges but by the movement of mobile ions toward the perovskite/transport layer interfaces, which inhibits charge extraction due to band flattening, which in turn leads to current losses. Finally, we generalized these findings to lead-based perovskites, showing that the loss mechanism is universal.<br/><br/>I will discuss the negative role mobile ions play in perovskite solar cells and how our findings pave the path towards understanding and mitigating a key loss mechanism. Furthermore, I will also give an outlook on what our results mean for perovskite-based tandem solar cells. I will demonstrate our progress on the development of efficient (&gt;24%) all-perovskite tandem cells and will discuss limitations due to the mobile ions in these devices, in addition to a subcell analysis of interfacial and bulk recombination losses.