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 energy-level 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 –CO 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.