Constructing Interfacial Prestress to Achieve Homogeneously Strained Perovskites

Vertically inhomogeneous strain within perovskite crystalline layers remains a critical barrier to achieving high efficiency and long-term stability in perovskite solar cells. Herein, we address this challenge by integrating ascorbyl glucoside into hydrothermally synthesized TiO₂ nanocrystals derived from TiCl₄ to reduce the surface energy of TiO₂ electron transport layer. The small surface energy establishes a liquid/solid/air interface, creating a dewetting effect to trigger stressed perovskite lattice at the bottom region. This design aligns with the liquid/air interface at the top, typically accompanied by formation of an inevitably strained top surface of the perovskite crystals. By precisely controlling crystallization dynamics of the liquid/solid/air interface, we successfully obtained a compressively strained perovskite film that is homogeneously strained throughout the out-of-plane direction. This uniform strain perovskite films deliver outstanding device performance, improving efficiencies to 25.34% of target from 23.20% of control for small-area devices (0.09 cm²), and 24.13% of target from 21.25% of control for large-area devices (1.00 cm²). Moreover, the optimized device demonstrate remarkable operational stability, retaining over 95% (T95) of its initial efficiency for over 2 000 h. The mechanically informed strategy introduces a new paradigm for strain engineering, offering valuable insights into the design of high performance perovskite photovoltaics.