Juan-Pablo Correa-Baena1 Mallory Jensen1 Sarah Wieghold1 Barry Lai2 Tonio Buonassisi1

1, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
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.