Imide-Functionalized Heteroarene-Based n-Type Terpolymers Incorporating Intramolecular Noncovalent Sulfur∙∙∙Oxygen Interactions for Additive-Free All-Polymer Solar Cells

The aggregation/crystallinity of classic n-type terpolymers based on naphthalene diimide and perylene diimide is challenging to tune due to their rigid and extended cores, leading to suboptimal film morphology. A new strategy for developing high-performance n-type terpolymers by incorporating imide-functionalized heteroarenes is reported here to balance crystallinity and miscibility without sacrificing charge carrier mobilities. The introduction of thienopyrroledione (TPD) into the copolymer f-BTI2-FT results in a series of terpolymers BTI2-xTPD having distinct TPD content. The irregular backbone reduces crystallinity, yielding improved miscibility with the polymer donor. More importantly, TPD triggers noncovalent S⋯O interactions, increasing backbone planarity and in-chain charge transport. Such interactions also promote face-on polymer packing. As a result, all-polymer solar cells (all-PSCs) based on BTI2-30TPD achieve an optimal power conversion efficiency (PCE) of 8.28% with a small energy loss (0.53 eV). This efficiency is substantially higher than that of TPD (4.4%) or a BTI2-based copolymer (6.8%) and is also the highest for additive-free all-PSCs based on a terpolymer acceptor. Moreover, the BTI2-30TPD cell exhibits excellent stability with the PCE retaining 90% of its initial value after 400 h of aging. The results demonstrate that random polymerization using imide-functionalized heteroarenes is a powerful approach to develop terpolymer acceptors toward efficient and stable all-polymer solar cell PSCs.