Simultaneously Enhancing Efficiency and Stability of Ternary Organic Solar Cells via a Benzothiadiazole-Thieno[3,2-c]isochromene-Based Small-Molecule Donor in the PTB7-Th:PC71BM System

The ternary strategy has emerged as an effective approach to enhance the photovoltaic performance of organic solar cells (OSCs), yet simultaneously improving both efficiency and stability remains a formidable challenge. Herein, we report a small-molecule donor (TiC12), featuring a thieno[3,2-c]isochromene unit, as a third component to fabricate ternary fullerene-based OSCs using the low-cost PTB7-Th:PC71BM host matrix. The influence of TiC12 on the active-layer morphology, device efficiency, and long-term stability is systematically investigated. The results reveal that the incorporation of TiC12 enables precise regulation of the blend film morphology, leading to a marked improvement in photovoltaic performance. Consequently, the optimized ternary devices achieve a notable power conversion efficiency (PCE) of 10.42%, which significantly surpasses that of the corresponding binary PTB7-Th:PC71BM counterparts (9.16%). More importantly, the ternary system simultaneously exhibits substantially enhanced operational stability, retaining 82.7% of its initial PCE after 2304 h under ambient storage in a N2-filled glovebox. This work demonstrates that TiC12, with its unique thieno[3,2-c]isochromene framework, represents a promising third-component candidate for achieving both high efficiency and superior stability in ternary fullerene OSCs.