Small-Molecule Acceptors with Asymmetric Thieno[3,2-c]isochromene Bridged Units for Boosting the Efficiency and Stability of Fullerene-Based Organic Solar Cells

Abstract

Ternary strategy is an effective approach to boost the photovoltaic performance of organic solar cells (OSCs). However, the ternary OSCs using a nonfullerene small-molecule acceptor (SMA) as the third component into the binary fullerene–donor system have not received satisfactory progress. Here, we developed a simple A–D–D′–D–A-type SMA of BDT–2TiC16–2CN, employing benzodithiophene (BDT) as an electron-donating (D′) centra, asymmetric bis(hexadecyl) thieno[3,2-c]isochromene (TiC) as an electron-donating (D) bridged unit, and cyanoindanone (CN) as a strong electron-withdrawing (A) terminal. Its thermal, optical, electrochemical, and photovoltaic properties were systemically studied. It is demonstrated that BDT–2TiC16–2CN exhibits absorption maxima at 703 nm as well as the cascaded HOMO and LUMO energy levels (−5.61/–3.96 eV) with polymers PM6 and PC71BM. Encouragingly, incorporating the BDT–2TiC16–2CN guest into the PM6:PC71BM blend, the ternary OSCs exhibit better photovoltaic properties and higher device stability than the binary OSCs. An improved PCE of 9.39% is obtained in the ternary OSCs, which is increased by 12.2% in comparison with that of the binary OSCs (8.37%). More importantly, 73.71% of the initial PCE is still maintained after 1440 h at room temperature and 67.22% after 1440 min at 65 °C. Our work indicates that BDT–2TiC16–2CN with an asymmetric TiC bridged unit is a potential SMA used as a third component to improve the device efficiency and stability for the ternary fullerene OSCs.