A small-molecule donor with thieno[3,2-c]isochromene unit to synchronously elevate efficiency and stability of ternary fullerene organic solar cells

Introducing a third component into bulk heterojunction organic solar cells (OSCs) has become an effective strategy to improve device efficiency. However, it is difficult to get ternary fullerene OSCs simultaneously with high device efficiency and stability. In this work, a small-molecule donor (TiC8) with thieno[3,2-c]isochromene unit was primarily reported as a third component to construct cascade ternary fullerene OSCs based on a typical low-cost PTB7-Th:PC71BM host matrix. The effect of TiC8 was deeply studied on active-layer morphology, device efficiency and stability. It is found that introducing the third component TiC8 is available to accurately manage active-layer morphology and improve device performance of the ternary OSCs based on the PTB7-Th:PC71BM host matrix. Furthermore, an increasing power conversion efficiency (PCE) of 11.12% was obtain in this type of ternary fullerene OSCs, which is significantly higher than those values in the corresponding binary fullerene OSCs with PTB7-Th:PC71BM (9.16%) or TiC8:PC71BM (4.53%) systems. More importantly, the device stability of the ternary fullerene OSCs was dramatically elevated at the same time. The transient PCE value maintained 80% level after 4752 h (156 days) at room temperature and 80.2% level after 432 h at 100 °C relative to the initial PCE for the ternary fullerene OSCs in the N2-filled glovebox. A high device efficiency and an unprecedented device stability are obtained in this type of ternary fullerene OSCs. Our work indicates that small-molecule donor TiC8 with thieno[3,2-c]isochromene unit is a promising the third component to promote the device performance with high PCE and outstanding device stability for ternary fullerene OSCs.