Cation Alloying Delocalizes Polarons in Lead-halide Perovskites
Résumé
Recently, mixed-cation perovskites have promised enhanced performances concerning stability and efficiency in optoelectronic devices. Here, we report a systematic study on the effects of cation alloying on polaronic properties in cation-alloyed perovskites using first principle calculations. We find that cation alloying significantly reduces the polaron binding energies for both electrons and holes compared to pure methylammonium lead iodide (MAPbI3). This is rationalized in terms of crystal symmetry reduction that causes polarons to be more delocalized. Electron polarons undergo large Jahn-Teller distortions (~15−30%) while hole polarons tend to shrink lattice by ~5%. Such different lattice distortion footprints could be utilized to distinguish the type of polarons. Finally, our simulations show that a Cs, formamidinium (FA) and MA mixture can effectively minimize polaron binding energy while weakly affecting band gap, in a good agreement with experimental findings. These modeling results can guide future development of halide perovskite materials compositions for optoelectronic applications.
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