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

Abstract

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 (CH3)PbI3 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.