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

Abstract

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 obtain ternary fullerene OSCs that simultaneously exhibit high device efficiency and stability. In this work, a small-molecule donor (TiC8) with a 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 on the active-layer morphology, device efficiency and stability was deeply studied. It is found that introducing the third component TiC8 is effective in accurately regulating the active-layer morphology and improving the device performance of the ternary OSCs based on the PTB7-Th:PC₇₁BM host matrix. Furthermore, an increased power conversion efficiency (PCE) of 11.12% was obtained in this type of ternary fullerene OSC, 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 improved at the same time. The PCE value was maintained at the 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 a N₂-filled glovebox. Our work indicates that small-molecule donor TiC8 with a thieno[3,2-c]isochromene unit is a promising third component to enhance the device performance with high PCE and outstanding device stability for ternary fullerene OSCs.