Abstract:

Organic solar cells (OSCs) have emerged as a core research direction in new energy materials due to their lightweight, flexibility, and solution-processability. Bulk heterojunction (BHJ)-based OSCs have achieved continuous performance breakthroughs with power conversion efficiency (PCE) exceeding 20% in recent years, laying a critical foundation for practical commercialization. However, device lifetime has become a key bottleneck restricting large-scale application: under long-term storage or photo-thermal aging conditions, the BHJ active layer suffers from performance degradation due to the instability of its nano-interpenetrating network morphology, mainly caused by the aggregation of small-molecule acceptors (SMAs) that form large-sized domains and structural defects, damaging charge transport channels. To address this stability challenge, the oligomerization modification strategy for SMAs has been proposed, yielding polymer and oligomer acceptors. While polymer acceptors improve active layer stability by increasing molecular weight, they suffer from broad molecular weight distribution and significant batch-to-batch differences due to fluctuating coupling efficiency, failing to meet large-scale preparation requirements. In contrast, oligomer acceptors (especially dimer acceptors with two repeating units) overcome these limitations with fixed molecular structures, simple synthesis without complex molecular weight regulation, minimized batch-to-batch deviations, and effective inhibition of small-molecule migration/aggregation, achieving a triple balance of stability, synthetic simplicity, and batch reproducibility. Additionally, dimer acceptors serve as ideal third components in binary active layers: they induce ordered π–π stacking via intermolecular non-covalent interactions, precisely regulate active layer crystal size to match exciton diffusion length, reduce charge transport losses, and compensate for binary systems' deficiencies in morphology regulation and performance stability. Currently, most reported dimer acceptors are based on fused-ring electron acceptors, featuring complex synthesis and high costs, while non-fused-ring electron acceptors offer simple design, few synthetic steps, and low cost via intramolecular non-covalent interactions (e.g., S…O, S…N interactions) and steric hindrance regulation. However, research on "non-fused-ring dimer acceptors" remains scarce, leaving a gap in combining non-fused-rings' low cost with dimers' lifetime and batch reproducibility advantages. To this end, this work designs and synthesizes a novel non-fused-ring dimer acceptor D-2BTH2F-H with simple preparation. The ternary OSCs based on D18:2BTH-2F: D-2BTH2F-H achieve a PCE of 17.95% and retain 80% of the initial efficiency after 1224 h of room-temperature storage, providing a new technical pathway for OSCs to balance low cost, high efficiency, long lifetime, and high batch reproducibility.

Key words: Organic solar cells, Nonfused ring electron acceptor, Dimeric electron acceptor, Ternary blend strategy, Device stability