Efficient All-Polymer Solar Cells Enabled by a Novel Medium Bandgap Guest Acceptor

Near-infrared (NIR)-absorbing polymerized small molecule acceptors (PSMAs) based on a Y-series backbone (such as PY-IT) have been widely developed to fabricate efficient all-polymer solar cells (all-PSCs). However, medium-bandgap PSMAs are often overlooked, while they as the third component can be expected to boost power conversion efficiencies (PCEs) of all-PSCs, mainly due to their up-shifted lowest unoccupied molecular orbital (LUMO) energy level, complimentary absorption, and diverse intermolecular interaction compared to the NIR-absorbing host acceptor. Herein, an IDIC-series medium-bandgap PSMA (P-ITTC) is developed and introduced as the third component into D18/PY-IT host, which can not only form complementary absorption and cascade energy level, but also finely optimize active layer morphology. Therefore, compared to the D18/PY-IT based parental all-PSCs, the ternary all-PSCs based on D18/PY-IT:P-ITTC obtain an increased exciton dissociation, charge transport, carrier lifetime, as well as suppressed charge recombination and energy loss. As a result, the ternary all-PSCs achieve a high PCE of 17.64% with a photovoltage of 0.96 V, both of which are among the top values in layer-by-layer typed all-PSCs. This work provides a method for the design and selection of the medium-bandgap third component to fabricate efficient all-PSCs.