Guanidinium Substitution Improves Self-Healing and Photodamage Resilience of MAPbI₃

Self-healing materials can become game changers for developing sustainable (opto)electronics. APbX₃ 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 Pb²⁺ 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).