High-performance flexible and air-stable perovskite solar cells with a large active area based on poly(3-hexylthiophene) nanofibrils

Flexible metal halide perovskite solar cells (PSCs) have been considered promising wearable energy power sources. Recently, various multi-functional charge-transporting layers, with high conductivity and air stability, have been rapidly developed in order to improve device performance. The practical use of flexible PSCs requires the retention of the performance and air stability at large active areas. However, increasing the size of the active layer results in increased contact and series resistance at the interfaces of the device. This hinders the charge transport, leading to charge recombination and degradation of the device performance. Furthermore, the poor stability of organic small molecules is detrimental to long-term stability. As such, flexible PSCs based on Li-doped poly(3-hexylthiopehene) (P3HT) nanofibrils (LN-P3HT), as a hole transporting layer (HTL), are prepared by subjecting a P3HT solution to a cooling process. The nanofibrils obtained via the π-conjugation of the thiophene rings result in improved conductivity and air stability, yielding high-performance, flexible, and air-stable PSCs with an active area of 1 cm 2 (PCE = 13.12%). This outstanding performance and mechanical stability are retained (PCE = 12.96%) after 500 bending cycles at r = 15 mm; these PSCs also exhibit a 30-day PCE retention of 87% (relative to the initial PCE) at a relative humidity of 30%. Therefore, this novel and facile strategy for preparing an efficient and air-stable organic HTL is a promising method for the realization of high-performance large-area flexible PSCs. By incorporating long P3HT nanofibrils as a hole transporting layer, high-performance, air-stable and flexible perovskite solar cells with a large active area (1 cm 2 ) have been realized with an excellent power conversion efficiency of 13.12%.