Ester Side Chains Engineered Quinoxaline Based D-A Copolymers for High-Efficiency All-Polymer Solar Cells

The simple ester side-chains strategy has been an effective approach in fine regulating electronic levels, intermolecular interaction, and aggregation morphology of organic photovoltaic materials, which makes for promoting the photovoltaic performance of organic solar cells (OSCs). Herein, two novel D-A conjugated polymers, namely PBQxBE and PBQxTE, are designed and synthesized, derived from an alkylthiothiophene benzodithiophene (BDTTS) as donor moiety, thiophene as the pi-bridges, and an identical molecular skeleton but different side chains based on quinoxaline (Qx) as acceptor units. The PBQxBE with ester engineered benzene side chains on the Qx unit exhibits better molecular flatness, stronger intermolecular interaction, and higher hole mobility than the analogous PBQxTE with ester engineered thiophene side chains. After combined with polymer acceptor PIDTC-T, the blend film of PBQxBE:PIDTC-T presented higher and balanced hole/electron mobility, better favorable aggregation morphology, as well as less charge carrier recombination. Thus, the all-polymer solar cells (all-PSCs) based on PBQxBE:PIDTC-T delivered a power conversion efficiency (PCE) of 10.17% with simultaneously increased basic parameters, which is much higher than that of 7.40% for the PBQxTE-based ones. The PCE of 10.17% is by far the highest values reported for all-PSCs from the Qx-based polymers as donor. The results demonstrate that the ester side-chains engineering of Qx-based polymers is an effective strategy to improve their photovoltaic performance of all-PSCs.