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-2,1,3benzothiadiazole (BTF 2 ) as the acceptor, with thiophene (T) and renewable resource materials, cardanol (C) and guaiacol (G) as the donor materials. The reference molecule, abbreviated as T 4 BTF 2 , is fully petro-sourced, while C 2 T 2 BTF 2 and G 2 T 2 BTF 2 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 G 2 T 2 BTF 2 is more highly planar than C 2 T 2 BTF 2 due to the difference in the positioning of the alkyl/alkoxy chain. With bulk heterojunction OSCs with PC 71 BM as the acceptor, G 2 T 2 BTF 2 exhibited a high V oc of 0.83 V among all the analyzed small molecules. When compared with the reference molecule T 4 BTF 2 , G 2 T 2 BTF 2 showed a high PCE of 5.56% with a high J sc of 10.98 mA/cm 2 and FF of 0.61, whereas the PCEs of T 4 BTF 2 and C 2 T 2 BTF 2 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.
To improve the power conversion efficiency (PCE) of the organic solar cells (OSCs), it is necessary to widen the absorption profile of the active layer. It is possible by using a ternary active layer consisting of either two donors (D) and one acceptor (A) or two acceptors and one donor having complementary absorption and appropriate frontier energy levels for efficient exciton generation and their dissociation into free charge carriers and subsequent charge/energy transfer. Herein, a large bandgap guaiacol‐based small molecule (SMD) is used as guest donor in ternary OSCs to improve the PCE and suppress the energy loss. SMD exhibits a lager bandgap and deeper highest occupied molecular orbital (HOMO) energy level compared with conjugated polymer donor (P). Therefore, the HOMO energy level is effectively down‐shifted when P is mixed with SMD, which is beneficial for attaining high open circuit voltage (VOC). OSCs based on the optimized ternary blend P:SMD:Y6 (0.8:0.2:1.2, w/w) after solvent vapor annealing attained a higher VOC of 0.85 V and low energy loss of 0.51 eV compared with the binary device P:Y6 (1:1.2, w/w) with VOC of 0.81 V and energy loss of 0.55 eV, delivering an overall PCE of 15.37%.
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