Rational design of flexible-linked 3D dimeric acceptors for stable organic solar cells demonstrating 19.2% efficiency

Abstract

Despite substantial improvements in the power conversion efficiencies (PCEs) of organic solar cells (OSCs), achieving long-term stability still presents a formidable challenge to their commercial viability. Inspired by the efficient and stable 3D dimeric acceptors of the CH8 series, we developed two dimeric acceptors, CH8-6 and CH8-7, by linking two monomers with flexible alkyl linkers. Interestingly, both the monomeric acceptor CH8-T and dimeric acceptor CH8-6 exhibited similar optical and electronic properties, including molecular absorption, energy levels, packing, and crystallinity, indicating that the incorporated linkers exerted minimal influence on the molecular properties. Such linkers could facilitate morphological optimization, enabling CH8-6- and CH8-7-based binary OSCs to achieve a better PCE than their corresponding mono-like molecules. Furthermore, adding L8-BO to the binary OSCs facilitated appropriate phase separation and order packing, allowing PM6:CH8-6:L8-BO ternary OSCs to achieve a record-high PCE of 19.2% for oligomeric acceptors. Moreover, incorporating a flexible linker suppressed molecular diffusion, stabilizing the active-layer morphology. Consequently, PM6:CH8-6 binary OSCs exhibited excellent thermal stability, while PM6:CH8-6 flexible OSCs also demonstrated remarkable mechanical flexibility, maintaining 96% of their initial PCE even after 1200 bending cycles. Therefore, this study presents a feasible approach to improve the PCE, stability, and flexibility of OSCs simultaneously.