Simple non-fused ring electron acceptors enables effective organic solar cells by employing heptan-3-yloxyl side chains

Abstract

Designing low-cost electron acceptors for effective bulk heterojunction (BHJ) organic solar cells (OSCs) is challenging. Here, we report two low-cost electron acceptors (TT-BO and TT-EH) with the same core of heptan-3-yloxylated thieno[3,2-b]thiophene, differing only in the alkylated thiophene-bridges. Both acceptors have similar low optical gaps (≈1.40 eV), but TT-EH exhibits a more ordered microstructure in thin film and higher electron mobility of 2.0 × 10−4 cm2 V−1 s−1 compared to TT-BO (1.7 × 10−4 cm2 V−1 s−1). After blending with the polymer donor, the TT-EH blend film shows a longer crystal coherence length of 2.4 nm for π-π stacking. Consequently, the TT-BO-based OSC achieves a 13.1 % power conversion efficiency (PCE). In contrast, the TT-EH-based OSC produces an excellent PCE of 14.2 %, the highest value among this kind of electron acceptors. This work offers a new insight into designing low-cost electron acceptors for efficient OSC.