(Invited) Ion Migration Influencing Perovskite Solar Cell Performance and Stability

The thermodynamic and redox properties of halide perovskites provide a strong driving force for hole trapping and oxidation of iodide species. When in contact with a non-polar solvent, the migration of iodine species is further extended to expulsion of iodine from the perovskite film. Thus, the mobility of halides and their susceptibility to hole-induced oxidation play a crucial role in determining the long-term stability of metal halide perovskite solar cells. When Ruddlesden-Popper 2D mixed-halide perovskite films with spacer cations such as butylammonium are introduced into three-dimensional (3D) perovskite films, they can stabilize them against moisture-induced degradation at room temperature. While such passivation of 3D perovskites using 2D perovskites has been reported widely, the instability of the 2D/3D interface during long term solar cell operation can be problematic, especially at higher temperatures. The cation migration under light and heat can significantly alter the 2D/3D interface, thus affecting the solar cell performance. We have now probed the cation migration between 2D and 3D perovskites by physically pairing X PbI (X=butylammonium BA, oleylammonium OA, or phenethylammonium PEA) 2D film and (CH 3 )PbI 3 3D film at different temperatures by recording changes in the absorption and emission spectra. Thus, suppression of halide ion migration as well as cation migration remains a key factor in achieving long term stability and improving efficiency of perovskite solar cells and light emitting devices.