A & X Ions Govern APbX₃ Halide Perovskite Self-Healing in Crystals & Films

Self-healing (SH) materials can become game changers in developing sustainable “stuff”, especially in (opto)electronics. In terms of sustainable use, APbX₃Halide (=X) Perovskite (HaP) semiconductors have a strong advantage over most others, as they can self-heal (SH) damage. We show SH, using "fluorescence recovery after photobleaching" (FRAP), also in (encapsulated) polycrystalline films, as used in most devices. There, SH from photodamage is faster for γ-CsPbI₃ and α-FAPbI₃than for MAPbI₃ and substituting ≧15 at.% MA⁺ with guanidinium (Gua⁺) or acetamidinium (AA⁺) enhances SH. However, substituting dimethyl ammonium (DMA⁺), about the size of Gua⁺ and AA⁺, for MA⁺ does not change the SH rate. Thus, while the A cation is considered electronically relatively inactive, it affects both SH kinetics (and photodamage thresholds). Based on the time scale of SH, we infer that the rate-determining step of SH involves short-range diffusion of A⁺ and/or Pb²⁺ cations, complementing earlier findings, and implicating halides (X^-) in SH. The SH rate correlates with the material’s strain, the A⁺ dipole moment, and A^{+ …..} I^- hydrogen bonding, offering clues to the roles of ion, electron, and energy migration in the SH mechanism, which will help guide the design of SH materials.<br/><br/>* Work done with DR Ceratti (now at ENSCParis), Y Soffer, S Bera, Y Feldman & M Elbaum, all from the Weizmann Inst.