Fig. 1. (Color online) (a) Giant switchable photocurrent curve in a non-selective contact structured device. Reproduced with permission^[2], Copyright 2014, Nature Publishing Group. (b) Schematic representation of ion migration in a perovskite solar cell when applying forward (left) and reverse bias (right). Reproduced with permission^[2], Copyright 2014, Nature Publishing Group. (c) The possible migrating paths for I vacancies, MA vacancies, Pb vacancies and I interstitial defects. Reproduced with permission^[4], Copyright 2015, The Royal Society of Chemistry. (d) Schematic diagrams indicating the influence of vacancy drift on the band energies of a p–i–n device at short circuit^[3].

Fig. 2. (Color online) (a) The 200 XRD peak of an x = 0.6 film before (black) and after (red) white-light soaking for 5 minutes at ~50 mW/cm². XRD patterns of an x = 0.2 film (dashed green) and an x = 0.7 film (dashed brown) are included for comparison. Reproduced with permission^[12], Copyright 2015, Royal Society of Chemistry. (b) Proposed mechanism of photo-induced cleaning by halide redistribution. Reproduced with permission^[15], Copyright 2016, Nature Publishing Group. (c) (d) Photoluminescence enhancement and quenching mechanisms. (c) Ion dynamics in MAPbI₃ thin film promoting PLIE, when the probability of I⁰ species encounters is small and Frenkel pair annihilation is boosted by electron trapping, and PLID (d) when the probability of I⁰ species encounters is high, boosting I₂ molecule formation. (c/d) Reproduced with permission^[16], Copyright 2019, Nature Publishing Group.