Fluorinated Cross-linkable and Dopant-free hole transporting materials for efficient and stable perovskite solar cells

Two novel hole transporting materials (HTMs) bearing thermally cross-linkable styryl groups were developed and applied for perovskite solar cells. These HTMs could be in situ cross-linked under mild temperature. The resulted cross-linked HTMs form smooth, solvent-resistant films, which enables the subsequent spin-coating of perovskite layer. In addition, the fluorination approach successfully leads to strong interactions between HTM, formamidine (FA) and lead in perovskite, resulting in the passivation of the perovskite film. The device using the HTM with fluorine moieties (HTM-F) showed higher power conversion efficiency (PCE) of 20.51% than that of the device using fluorine-free HTM (HTM-H) of 19.07%. Moreover, the device with HTM-F exhibits better stability, retaining 90% of the initial PCE after 2000 h under ambient air and 91% of the initial PCE after 1000 h under 85 °C heating.