Revealing and Inhibiting the Facet-related Ion Migration for Efficient and Stable Perovskite Solar Cells.

Ion migration is a major issue hindering the long-term stability of perovskite solar cells (PSCs). As an intrinsic characteristic of metal halide perovskite materials, ion migration is closely related to the atomic arrangement and coordination, which are the basic characteristic differences among various facets. Herein, we report the facet-related ion migration, and then achieve the inhibition of ion migration in perovskite through finely modulating the facet orientation. We show that the (100) facet is substantially more vulnerable to cationic migration than the (111) facet. The main reason for this difference in migration is that the cationic migration route in the (111) facet deviates from that in the (100) facet, which increases the active migration energy and weakens the contribution from the electric field during operation. We prepare a (111)-dominated perovskite film by incorporating a facile and green addition of water (HO) into the antisolvent, further achieving a power conversion efficiency (PCE) of 26.0 % (25.4 % certification) on regular planar PSCs and 25.8 % on inverted PSCs. Moreover, the unencapsulated PSCs can maintain 95 % of their initial PCE after 3500-hours operation under simulated AM1.5 illumination at the maximum power point.