| Summary: | Abstract Achieving an ideal morphology is an imperative avenue for enhancing key parameters toward high‐performing organic solar cells (OSCs). Among a myriad of morphological‐control methods, the strategy of incorporating a third component with structural similarity and crystallinity difference to construct ternary OSCs has emerged as an effective approach to regulate morphology. A nematic liquid‐crystalline benzodithiophene terthiophene rhodamine (BTR) molecule, which possesses the same alkylthio‐thienyl‐substituted benzo moiety but obviously stronger crystallinity compared to classical medium‐bandgap polymeric donor PM6, is employed as a third component to construct ternary OSCs based on a PM6:BTR:Y6 system. The doping of BTR (5 wt%) is found to be enough to improve the OSC morphology—significantly enhancing the crystallinity of the photoactive layer while slightly reducing the donor/acceptor phase separation scale simultaneously. Rarely is such a morphology evolution reported. It positively affects the electronic properties of the device—prolongs the carrier lifetime, shortens the photocurrent decay time, facilitates exciton dissociation, charge transport, and collection, and ultimately boosts the power conversion efficiency from 15.7% to 16.6%. This result demonstrates that the successful synergy of liquid‐crystalline small‐molecule and polymeric donors delicately adjusts the active‐layer morphology and refines device performance, which brings vibrancy to the OSC research field.
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