Guanidinium-mediated crystallization modulation for high-performance indoor flexible perovskite solar cells

Lightweight flexible perovskite solar cells (F-PSCs) have emerged as a commercially promising candidate for indoor energy harvesting applications. However, solution-processed fabrication induces deep-level trap states within perovskite films, posing constraints on both power conversion efficiency (PCE) and operational durability of devices. Herein, we developed a ligand-mediated crystallization modulation strategy that simultaneously optimizes the growth quality of perovskite on flexible substrates and deciphers the structure-performance correlations. Guanidinium incorporation promotes a more than threefold increase in grain sizes of perovskite films by refining the crystallization rate. These enlarged crystals function as the oriental scaffolding to improve the interface adhesion, residual strain, and trap density within the modified films, thus ensuring efficient charge transfer and extraction. The resultant devices achieved a champion efficiency of 42.8% under 1000 lux white LED illumination, recording as among the highest efficiencies for indoor F-PSCs. Furthermore, the device stability under potential operational conditions, including ambient exposure, continuous illumination, and mechanical bending, was collectively improved. This work elucidates the crystallization mechanism governing structural resilience and carrier kinetics in F-PSCs, providing a practical methodology for high-efficiency and stable indoor photovoltaics.