The Emergence of BLZ‐20: A Novel Wide‐Bandgap Donor Polymer Achieving a Record 20.55% Efficiency in Organic Solar Cells

To address the critical challenge of the scarcity of low-cost wide-bandgap polymer donor materials, we have developed a novel ester-substituted benzotrithiophene acceptor unit. The incorporation of an ester group into the benzotrithiophene structure induces a fundamental transformation, shifting it from an electron-donating entity to a weakly electron-withdrawing one. Leveraging this innovation, we synthesized a new low-cost wide-bandgap polymer donor material, namely BLZ-20, by using the ester-functionalized benzotrithiophene as the acceptor unit, benzodithiophene (BDT) as the donor unit, and 3-alkylthiophene as the π-bridge. BLZ-20 exhibits excellent solution-processability and unique temperature-dependent aggregation properties. Building on these advantageous characteristics, the BLZ-20:L8-BO blend film exhibits a well-defined nanofiber network structure that not only promotes efficient exciton dissociation and charge transport but also effectively reduces nonradiative losses. The BLZ-20:L8-BO-based binary organic solar cell (OSC) has achieved a remarkable power conversion efficiency (PCE) of 20.13%, setting a new industry-wide benchmark for OSCs. Furthermore, the BLZ-20:L8-BO:BTP-eC9-based ternary OSC has attained an even more impressive PCE of 20.55%, ranking among the highest-performing OSCs ever reported. Our research findings unequivocally demonstrate that the wide-bandgap polymer BLZ-20, derived from benzotrithiophene, is a cost-effective and high-performance donor material. It offers significant potential for advancing the practical application of OSCs.