LAUSR

Abstract Small organic hole-transporting materials, such as the state-of-the-art spiro -OMeTAD, have been effectively employed in perovskite solar cells. However, these hole-transporting materials are prone to crystallize due to their high molecular symmetry, which is not conducive to forming dense films and further affects the stability of the devices. Herein a novel hole-transporting material (Z1) is assembled with double carbazole-based backbones and five electron-donors. Reference molecule Z2 with fewer electron-donors, and X2 with higher symmetry, are introduced as direct comparisons in reproducible outperformance. Z1 gives a more efficient hole-transfer than Z2, and a more uniform and stable amorphous film than X2. In addition, although Z1 presents a twisted V-shaped lower symmetrical structure, it still exhibits high conductivity and hole-mobility, which arises from the molecular polarization induced by the electronegative carbazole units and multiple electropositive electron-donors. When employed in solar devices, Z1 achieves a power conversion efficiency up to 18.57% without current hysteresis. More importantly, the doped-Z1 device maintains 72% of initial efficiency over 144 days of storage without encapsulation, whereas the device made of doped spiro -OMeTAD vanishes after 134 days.