Cation Exchange at the 2D/3D Perovskite Interface and its Impact on Solar Cell Performance

Ruddlesden-Popper 2D mixed-halide perovskite films with spacer cations such as butylammonium and Dion-Jacobson 2D mixed-halide perovskite films with 1,4-phenylenedimethanammonium are used to stabilize the performance of perovskite solar cells. The cation migration under operation of the solar cell can significantly alter the 2D/3D interface. 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 (CH₃NH₃)PbI 3D film at different temperatures by recording changes in the absorption and emission spectra. The migration of methyl ammonium towards the 2D film slowly converts n=1 layered structure into n=2 and 3 layered films. The 3D film on the other hand, exhibits relatively small changes. In addition, we have also correlated the migration of cations to the performance of solar cells. The ease of migration of spacer cations between physically paired films suggest that the varied composition at the interface should be considered while evaluating the effectiveness of 2D/3D design strategy for improving the performance of perovskite solar cells