Cardanol- and Guaiacol-Sourced Solution-Processable Green Small Molecule-Based Organic Solar Cells

An environmentally compatible organic solar cell (OSC) has potential to build a global clean energy infrastructure for the world. However, much less attention has been focused on the structures sourced from greener origins to enhance the sustainability aspect of these devices. Herein, we report a rational design, synthesis, and characterization of donor (D)-acceptor (A)-based green organic small molecules, consisting of difluoro-2,1,3-benzothiadiazole (BTF2) as the acceptor, with thiophene (T) and renewable resource materials, cardanol (C) and guaiacol (G) as the donor materials. The reference molecule, abbreviated as T4BTF2, is fully petro-sourced, while C2T2BTF2 and G2T2BTF2 are partly renewable origin molecules. Broad and strong absorption characteristics ranging from 300 to 600 nm along with high thermal stability are supportive for utility of the green origin small molecules in solar cells. Density functional theory (DFT) calculations revealed that G2T2BTF2 is more highly planar than C2T2BTF2 due to the difference in the positioning of the alkyl/alkoxy chain. With bulk heterojunction OSCs with PC71BM as the acceptor, G2T2BTF2 exhibited a high V oc of 0.83 V among all the analyzed small molecules. When compared with the reference molecule T4BTF2, G2T2BTF2 showed a high PCE of 5.56% with a high J sc of 10.98 mA/cm2 and FF of 0.61, whereas the PCEs of T4BTF2 and C2T2BTF2 are 3.98% and 3.23%, respectively. Our work demonstrates a rational approach to synthesize and develop green organic semiconductors using the biofeedstock derived starting materials for realizing efficient and environment compatible OSCs.