Thermotropic liquid-assisted interface management enables efficient and stable perovskite solar cells and modules

Despite substantial improvements in the quality of perovskite films achieved through processing optimization, the prevalence of surface and interfacial defects underscores the critical need for efficient post-treatment strategies. Here, we report an expectable surface engineering approach using thermotropic liquid molecule 1-boc-piperazine (1-BP). The 1-BP undergoes a solid-to-liquid phase transition and spontaneously migrates to perovskite grain boundaries during annealing process, forming an active encapsulation layer that reconstructs the perovskite interface. The most attractive achievement of ion migration suppression by 1-BP has been evidentially revealed by the in-situ time-of-flight secondary ion mass spectrometry. Base on the approach, the n-i-p perovskite solar cells achieve a certified power conversion efficiency of 25.62%, with perovskite solar modules achieving PCE of 22.03% (active area: 22.8 cm2). Furthermore, the 1-BP engineered devices demonstrated exceptional stability, retaining T90 after 1500 h at 65 °C with continuous illumination and T87 after 1000 h at 85 °C/85% RH. In this work, Chang et al. report a thermotropic liquid additive for perovskite solar cells that enables dynamic interface management, simultaneously passivating defects and suppressing ion migration to deliver high efficiency and substantially enhanced operational stability.