Uniaxial‐Oriented Perovskite Films with Controllable Orientation

Abstract Perovskite films with large crystal size, preferred orientation, and facile fabrication process, combining advantages of single‐crystal and polycrystalline films, have gained considerable attention recently. However, there is little research on the facet properties of perovskite films. Here, (111)‐ and (001)‐oriented perovskite films with bandgaps ranging from 1.53 to 1.77 eV, and systematically investigated their orientation‐dependent properties are achieved. The (111)‐oriented films show electron‐dominated traps and the (001)‐oriented films show hole‐dominated traps, which are related to their atomic arrangement at the surface. Compared with the (001)‐oriented films, the (111)‐oriented films exhibit lower work function and superior water/oxygen robustness. For the wide‐bandgap films, the lattice of the (001)‐oriented film provides an unobstructed passage for ion migration. Comparably, the (111)‐oriented films exhibit suppressed ion migration and excellent phase stability. The optimized unencapsulated solar cells based on both (001) and (111) orientations show a similar high efficiency of ≈23%. The (111)‐oriented solar cell exhibits excellent stability, maintaining 95% of its initial efficiency after 1500 h maximum power point (MPP) tracking test, and 97% initial efficiency after 3000 h aging in ambient conditions. This work paves the way for the rational design, controllable synthesis, and targeted optimization of uniaxial‐oriented perovskite films for various electronic applications.