Guanidinium Substitution Improves Self-Healing and Photodamage Resilience of MAPbI.

Self-healing materials can become game changers for developing sustainable (opto)electronics. APbX halide (=X) perovskites, HaPs, have shown a remarkable ability to self-heal damage. While we demonstrated self-healing in pure HaP compounds, in single crystals, and in polycrystalline thin films (as used in most devices), HaP compositions with multiple A (and X) constituents are preferred for solar cells. We now show self-healing in mixed A HaPs. Specifically, if at least 15 atom % of the methylammonium (MA) A cation is substituted for by guanidinium (Gua) or acetamidinium (AA), then the self-healing rate after damage is enhanced. In contrast, replacing MA with dimethylammonium (DMA), comparable in size to Gua or AA, does not alter this rate. Based on the times for self-healing, we infer that the rate-determining step involves short-range diffusion of A and/or Pb cations and that the self-healing rate correlates with the strain in the material, the A cation dipole moment, and H-bonding between A and I. These insights may offer clues for developing a detailed self-healing mechanism and understanding the kinetics to guide the design of self-healing materials. Fast recovery kinetics are important from the device perspective, as they allow complete recovery in devices during operation or when switched off (LEDs)/in the dark (photovoltaics).