LAUSR

Metal halide perovskites are promising as next‐generation photovoltaic materials, but stability issues are still a huge obstacle to their commercialization. Here, the formation and evolution of cracks in perovskite films during thermal cycling, which affect their mechanical stability, are investigated. Compressive strain is employed to suppress cracks and delamination by in situ formed polymers with low elastic modulus during crystal growth. The resultant devices pass the thermal‐cycling qualification (IEC61215:2016), retaining 95% of the initial power conversion efficiency (PCE) and compressive strain after 230 cycles. Meanwhile, the p–i–n devices deliver PCEs of 23.91% (0.0805 cm2) and 23.27% (1 cm2). The findings shed light on strain engineering with respect to their evolution, which enables mechanically stable perovskite solar cells.