Precise Morphology Control via Backbone‐Derived Solid Additive Enables Binary Organic Solar Cells to Achieve 20% Efficiency and Thick‐Film Compatibility

Abstract

Abstract Precise control of active layer morphology is essential for advancing organic solar cells (OSCs) toward practical applications. Here, a generalizable morphology regulation strategy is proposed using a structurally tailored crystallization template derived from the polymer donor backbone. A small molecule, BDD‐C6, is designed by extracting the benzodithiophene (BDD) unit from PM6 and appending an alkylated thiophene terminal. When incorporated into PM6:L8‐BO and PM6:BTP‐eC9 binary blends, compatibility studies and cross‐sectional absorption analysis reveal a favorable vertical phase distribution on alcohol‐soluble substrates. Thermodynamic evaluations confirm the good thermal stability and crystallinity of BDD‐C6. Crystallization kinetics and morphological characterizations investigations further show that BDD‐C6 delays film formation and promotes polymer ordering, thus extending exciton diffusion length. As a result, PM6:L8‐BO‐based binary device delivers a power conversion efficiency (PCE) of 19.81% in thin films and maintains a PCE of 16.93% even at a 400 nm thickness. Moreover, PM6:BTP‐eC9‐based OSCs present an efficiency of over 20%. Extending this strategy to D18 systems using a DTBT‐C6 small molecule similarly enhances morphology and device performance, realizing a PCE of 20.18% in D18:L8‐BO binary device. This work offers a backbone‐derived crystallization template strategy for the scalable fabrication of high‐efficiency OSCs