Stereoscopic Polymer Network for Developing Mechanically Robust Flexible Perovskite Solar Cells with an Efficiency Approaching 25%

Flexible perovskite solar cells (pero-SCs) have the potential to overturn the application scenario of silicon photovoltaic technology. However, their mechanical instability severely impedes their practical applicability, and the corresponding intrinsic degradation mechanism remains unclear. In this study, the degradation behavior of flexible pero-SCs is systematically analyzed under mechanical stress and it is observed that the structural failure first occurs in the polycrystal perovskite film, then extend to interfaces. To suppress the structural failure, pentaerythritol triacrylate, a crosslinked molecule with three stereoscopic crosslink sites, is employed to establish a 3D polymer network in both the interface and bulk perovskite. This network reduced the Young's modulus of the perovskite and simultaneously enhanced the interfacial toughness. As a result, the formation of cracks and delamination, which occur under a high mechanical stress, is significantly suppressed in the flexible pero-SC, which consequently retained 92% of its initial power conversion efficiency (PCE) after 20 000 bending cycles. Notably, the flexible device also shows a record PCE of 24.9% (certified 24.48%).