Enhanced charge carrier lifetime and mobility as a result of Rb and Cs incorporation in hybrid perovskite

Alkali addition in organic-inorganic perovskite has become the standard recipe for achieving solar cells with efficiencies exceeding 20%, but the mechanism is not well understood. We use non-contact carrier lifetime measurements, mobility measurements, and synchrotron-based x-ray characterization techniques to show that there is a unique benefit to adding hybrid perovskite samples with Rb and Cs simultaneously. When either Rb or Cs is added, charge carrier mobility increases with alkali concentration. Charge carrier lifetime benefits from alkali incorporation as well, but is optimized with only moderate concentration at 1%. When both Rb and Cs are introduced, however, the high mobility is maintained and the charge carrier lifetime increases considerably. Our results show that when incorporated alone, Rb and Cs have very similar roles in a perovskite crystal, but when co-added, halide distribution becomes homogenized correlating with improved charge transport properties.

Automated summary

Adding both Rb and Cs simultaneously to hybrid perovskite samples has been shown to increase carrier mobility and lifetime significantly, leading to improved charge transport properties. The roles of Rb and Cs in a perovskite crystal are similar when added alone, but their co-addition results in homogenized halide distribution, which is correlated with enhanced charge transport.