Dual-asymmetric backbone constructed polymerized small molecule acceptors for efficient all-polymer solar cells

Side-chain engineering and asymmetric backbone design have been proven to effectively improve the photovoltaic performance of polymerized small molecule acceptors (PSMAs) in all-polymer solar cells (all-PSCs). However, the reported PSMAs all independently use the above strategies, making it difficult to finely tune their optoelectronic properties. Here, we develop three near-infrared (NIR)-absorbing PSMAs (including asymmetric PY1S1Se-C11, dual-asymmetric PY1S1Se-C9 and PY1S1Se-BO) by sharing the same selenophene-fused asymmetric backbone but different unidirectional side-chains, which allows fine tailoring of their molecular energy level, crystallinity, and intermolecular interaction. Among their binary active layers, PBQx-TF:PY1S1Se-BO shows optimized morphology and charge transport compared to PBQx-TF:PY1S1Se-C9 and PBQx-TF:PY1S1Se-C11. Consequently, the PY1S1Se-BO-based binary all-PSCs achieve an improved power conversion efficiency (PCE) of 14.31% with both higher photovoltage and photocurrent values compared to the devices based on PY1S1Se-C9 (11.95%) and PY1S1Se-C11 (13.06%). Inspired by its NIR-absorption and high PCE, PY1S1Se-BO is introduced into binary PBQx-TF:PY-IT to construct ternary all-PSCs, achieving a superior PCE of 17.28% mainly due to their matched energy levels and complementary absorption. The above results indicate that our developed NIR-absorbing dual-asymmetric PY1S1Se-BO is a promising candidate for constructing efficient all-PSCs.