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The ternary strategy has proven to be an effective method for improving the efficiency of organic solar cells (OSCs). However, designing and selecting the third component still pose challenges. In this study, this issue is addressed by focusing on the PBDB‐T:Y18‐F binary system and introducing a new, strong luminescent, asymmetric small‐molecule acceptor (SMA) called L8‐CBIC‐Cl, which shares a similar skeleton with Y18‐F. The similarity in molecular framework facilitates good compatibility between the two acceptors, resulting in the formation of an alloy‐like acceptor phase. Furthermore, the norbornenyl‐modified end group in L8‐CBIC‐Cl contributes to its strong luminescent properties, which in turn leads to a low non‐radiative energy loss and a high open‐circuit voltage. Consequently, the PBDB‐T:L8‐CBIC‐Cl:Y18‐F based ternary devices realize a high power conversion efficiency (PCE) up to 17.01%, which is higher than PBDB‐T:Y18‐F device (14.49%). Importantly, L8‐CBIC‐Cl exhibits a good universality as a guest acceptor in other three binary systems (D18:Y6, D18:BTP‐eC9‐4F, and D18:L8‐BO). The D18:L8‐BO:L8‐CBIC‐Cl device shows an impressive efficiency of 19%. The work demonstrates that employing SMA with a high PLQY and better miscibility with host acceptor as the third component has a great potential for developing high‐efficiency ternary OSCs. [ABSTRACT FROM AUTHOR]

Here, a near‐infrared (NIR)‐absorbing small‐molecule acceptor (SMA) Y‐SeNF with strong intermolecular interaction and crystallinity is developed by combining selenophene‐fused core with naphthalene‐containing end‐group, and then as a custom‐tailor guest acceptor is incorporated into the binary PM6:L8‐BO host system. Y‐SeNF shows a 65 nm red‐shifted absorption compared to L8‐BO. Thanks to the strong crystallinity and intermolecular interaction of Y‐SeNF, the morphology of PM6:L8‐BO:Y‐SeNF can be precisely regulated by introducing Y‐SeNF, achieving improved charge‐transporting and suppressed non‐radiative energy loss. Consequently, ternary polymer solar cells (PSCs) offer an impressive device efficiency of 19.28% with both high photovoltage (0.873 V) and photocurrent (27.88 mA cm−2), which is one of the highest efficiencies in reported single‐junction PSCs. Notably, ternary PSC has excellent stability under maximum‐power‐point tracking for even over 200 h, which is better than its parental binary devices. The study provides a novel strategy to construct NIR‐absorbing SMA for efficient and stable PSCs toward practical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three small molecular acceptors were designed and synthesized. • Noncovalent Conformational Locks and Side-Chain Engineering can adjust the properties of acceptors. • Significantly different power conversion efficiencies of 12.09%, 12.30% and 14.25% are achieved. Three novel small molecular acceptors (SMAs) BO-2F , BO-C8-2F and BO-C2C6-C8-2F were designed and synthesized. These acceptors all possess planar molecular backbone because of the introduction of intramolecular noncovalent interaction. Among them, BO-C2C6-C8-2F with four side chains, which has the highest solubility, can form more appropriate nanomorphology when blending with PBDB-T. Hence, organic solar cells (OSCs) based on PBDB-T: BO-C2C6-C8-2F displayed an outstanding power convesion efficiency (PCE) of 14.25%, which is higher than BO-2F and BO-C8-2F based ones. To the best of our knowledge, the PCE of 14.25% is one of the highest for the OSCs based on A-π-D-π-A type SMAs. Our results have demonstrated that the combination of side-chain engineering and intramolecular conformation lock has a great prospect in the design of high performance SMAs for OSCs. [ABSTRACT FROM AUTHOR]