Green-solvent Processable Dopant-free Hole Transporting Materials for Inverted Perovskite Solar Cells.

The commercialization of perovskite solar cells (PVSCs) urgently requires the development of green-solvent processable dopant-free hole transporting materials (HTMs). However, strong intermolecular interactions that ensure high hole mobility always compromise the solubility and film-forming ability in green solvents. Herein, we show a simple but effective design strategy to solve this trade-off, that is, constructing star-shaped D-A-D structure. The resulting HTMs (BTP1-2) can be processed by green solvent of 2-methylanisole (2MA), a kind of food additive, and show high hole mobility and multiple defect passivation effects. An impressive efficiency of 24.34 % has been achieved for 2MA-processed BTP1 based inverted PVSCs, the highest value for green-solvent processable HTMs so far. Moreover, it is manifested that the charge separation of D-A type HTMs at the photoinduced excited state can help to passivate the defects of perovskites, indicating a new HTM design insight.