DOI: https://doi.org/10.29363/nanoge.hpatom.2022.018
Publication date: 30th October 2021
Lead halide perovskites have attracted great interest due to their possible application in solar cells, providing excellent power conversion efficiencies (PCE) of currently up to 25.7 % combined with simple and low-cost production procedures. We recently implemented an analytical approach based on 1H DQ NMR spectroscopy and MD simulations to investigate the mixing behaviour of A cations in FA/MA lead halide perovskites. Our investigations revealed that inhomogeneities in composition occur leading to a microstructure with MA- and FA-rich regions in the perovskite particles, while the reorientational cation dynamics seem to stay isotropic. The picture changes upon additionally mixing Br‑ ions in the system, which significantly increases the average cation-cation interaction strength indicating a restriction or partial immobilization of the cation dynamics. Here, we investigate the influence of halide mixing on the MA dynamics in mixed-halide MAPbI3-xBrx systems. We observe a surprising trend of the average H-H dipolar coupling strength of the MA cations as a function of Br‑ content. First MD simulations of mixed halide models suggest preferred orientations of the MA molecules in mixed halide environments causing an anisotropic reorientational motion. Our results shed light on the MA cation dynamics, which are discussed to influence charge carrier lifetimes, as well as halide demixing processes observed upon illumination, and therefore, will help to further exploit the full optoelectronic potential with respect to tandem solar cell designs.