Designing simple non-fused terthiophene-based electron acceptors for efficient organic solar cells

Low-cost photovoltaic materials are essential for realizing large-scale commercial applications of organic solar cells (OSCs). However, highly efficient OSCs based on low-cost photovoltaic materials are scarce due to a deficiency in understanding the structure-property relationship. Herein, we investigated two low-cost terthiophene-based electron acceptors, namely, 3TC8 and 3TEH, with 3,4-bis(octan-3-yloxy)thiophene, differing only in the alkylated thiophene-bridges. Both acceptors exhibit low optical gaps (∼1.43 eV) and possess deep highest occupied molecular orbital (HOMO) levels (∼−5.8 eV). Notably, the single-crystal structure of 3TEH demonstrates highly planar conjugated backbone and strong π-π stacking between intermolecular terminal groups, attributed to the presence of the bulky alkylated noncovalently conformational locks. Upon utilizing both acceptors to fabricate OSCs, the 3TC8-based device exhibited a power conversion efficiency (PCE) of 11.1%, while the 3TEH-based OSC demonstrated an excellent PCE of 14.4%. This PCE is the highest among OSCs based on terthiophene-containing electron acceptors. These results offer a new strategy for designing low-cost electron acceptors for highly efficient OSCs.