Alkoxy Side-Chain Engineering of Quinoxaline-Based Small Molecular Acceptors Enables High-Performance Organic Solar Cells

Alkoxy side-chain engineering is an effective strategy for constructing efficient organic photovoltaic materials. Here, we develop three A-DA'D-A type small molecule acceptors (SMAs) with different alkoxy chains substituted on quinoxaline (Qx) central cores, named BQO-C2, BQO-C4, and BQO-C6. The different lengths of alkoxy chains on the Qx core exhibit critical effects on the physicochemical properties, active layer morphology, and photovoltaic properties of resultant SMAs. BQO-C2 with shorter alkoxy chains demonstrates down-shifted energy levels, more planar molecular configuration, and stronger crystallinity compared to its two counterparts. Benefiting from the preferred face-on molecular packing orientation and better active layer morphology, the PBDB-T:BQO-C2-based device shows more efficient exciton dissociation, higher and more balanced charge carrier mobility, suppressed recombination, and thus a much higher power conversion efficiency (PCE) of 14.65% than BQO-C4- (PCE = 8.93%) and BQO-C6-based (PCE = 8.45%) devices. This work reveals the structure-performance relationship of alkoxy chain-substituted Qx-based SMAs, which provides important guidelines for the further design of high-performance active layer materials.