Functional role of dihalogenated benzothiadiazole volatile solid additives on crystallization in photoactive for high-performance organic solar cells

Abstract

Halogenated volatile solid additives (VSAs) can strategically properly control the active layer morphology to achieve high-performance organic solar cells (OSCs). In particular, fluorinated benzothiadiazole (FBT) VSAs, which have partial structural similarity to the active layer, previously demonstrated great potential for facilitating the intermolecular interaction, but still suffered from suboptimal morphology regulation, thus limiting power conversion efficiencies (PCEs). Herein, we have conducted an in-depth investigation on three dihalogenated BT VSAs (difluoro-BT (BT-2F), dichloro-BT (BT-2Cl), and dibromo-BT (BT-2Br)) to optimize the performance of PM6:L8-BO-based OSC platform. Relative to BT-2F and BT-2Cl VSAs, BT-2Br has superior donor/ acceptor interactions, which can yield a well-ordered morphology through kinetic control of active layer's crystallization during film formation, ultimately leading to enhanced charge transport performance. As a result, the BT-2Br-processed PM6:L8-BO-based OSC delivers a high PCE of 19.11 % with an excellent fill factor (FF) of 80.15 %, outperforming the reference OSCs (PCE: 18.31 %, FF: 76.28 %). This work provides a foundational framework for rationally halogenated solid additive engineering toward the development of high-efficiency OSCs.