Wide-Bandgap Dithienophthalimide-Based Polymer as an Effective Third Component for Efficient and Stable Organic Solar Cells

Ternary strategies are effective approaches to boost solar cell performance by introducing a third component as the guest, while selection of the simple component is yet a key issue. Herein, a low-cost dithienophthalimide (DPI)-based wide-bandgap polymer donor PBDT(8,10)-DPI(4,6) was selected as a third component for the host PM6:BTP-eC9 system. The effects of the third component on the optical and electrical properties, photovoltaic performance, and thin-film structure were explored. By incorporating a small amount of PBDT(8,10)-DPI(4,6) into the PM6:BTP-eC9 host, a broader absorption range, a cascaded energy level alignment, and a more favorable active layer morphology are achieved in ternary devices, leading to an improved short-circuit current density and fill factor. As a result, a PCE of 18.15% with a VOC of 0.86 V, a JSC of 27.35 mA cm–2, and an FF of 77.01% was ultimately achieved in the ternary device after adding 5% PBDT(8,10)-DPI(4,6), surpassing the efficiency (17.26%) of the control binary device. Meanwhile, the effect of the third component on device stability was investigated, revealing notable enhancements in overall stability (photostability, thermal stability, and storage stability) for the ternary devices. Thus, dithienophthalimide (DPI)-based polymer donors would be expected to be effective third components for efficient and stable organic solar cells.