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

ABSTRACT

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.