2, Argonne National Laboratory, Argonne, Illinois, United States
Perovskite solar cells have shown remarkable efficiencies beyond 21%, through organic and inorganic cation alloying. However, the role the inorganic cations plays is not well-understood. By using synchrotron-based micro X-ray fluorescence, we show that alkali metals K, Rb and Cs, mostly segregate into well-defined pockets without fully incorporating. In this presentation I will show how these alkali metals influence the distribution of other elements and how that improves electronic dynamics, including lifetimes above 3 µs and homogenous photobleaching in transient absorption visualized by ultrafast microscopy. Solar cell performance is compromised by large amounts of Rb/K and high efficiency is seen with small amounts of the alkali metal. Remarkably, the high concentration of Rb and K agglomerations do not affect the open-circuit voltage, average lifetimes and photoluminescence distribution, further indication of perovskite’s defect tolerance.