Residual Strain Evolution in Perovskite Solar Cells throughout Fabrication to Operation: Mechanisms, Characterization, and Regulation

Perovskite solar cells (PSCs) have achieved a power conversion efficiency (PCE) of over 27%, but further improvements of both PCEs and stability are needed for commercialization. One of the key factors hindering their development is the unpredictable residual strain in perovskites. The unstable octahedral structure of the perovskite cage leads to easy changes in bond lengths, bond angles, and crystal structure. It in turn generates, accumulates, and causes the non-uniform distribution of residual strain, ultimately affecting device performance. Therefore, given the versatility and precise tunability, residual strain engineering provides an effective pathway to optimize the performance of PSCs. This review summarizes the causes of residual strain during device fabrication and operation, qualitative/quantitative/auxiliary characterization methods, and various effective strain regulation methods in the past two years. Finally, unresolved scientific issues and future research directions in strain engineering are discussed. This comprehensive review aims to provide researchers with the latest advances in strain engineering, deepen fundamental understanding of strain effects, and eventually help enhance the performance of PSCs.