Hydroxylated non-fullerene acceptor for highly efficient inverted perovskite solar cells

Inverted perovskite solar cells (i-PSCs) manifest negligible hysteresis and potential to construct tandem solar cells attracting much attention, but their power conversion efficiency (PCE) still lags behind those of conventional ones due to non-radiative recombination from defect states and mismatched energylevel alignment for electron transport. Herein, we report on employing a hydroxylated non-fullerene acceptor (NFA), termed IT-DOH, to modify the interface between the perovskite and the electron transport layer (ETL) for reduced defects and improved electron transport. Compared with -CN and -C=O groups in the parent molecule ITIC, additional -OH groups in IT-DOH can further suppress defect states by interacting with undercoordinated Pb2+. More importantly, the conjugated planes of IT-DOH can be elongated by intermolecular hydrogen-bonding interactions, leading to a long-range-ordered molecular arrangement and face-on orientation, which facilitates the electron transport from the perovskite to the ETL through IT-DOH molecules. Consequently, a record PCE of 22.09% among reported i-PSCs modified by NFAs is achieved from IT-DOH-treated i-PSCs. Our work highlights the importance of molecular ordering and orientation of the NFAs as interfacial materials, and provides a guideline to design NFAs by hydroxylation for highly efficient and stable i-PSCs.