Small molecules based on tetrazine unit for efficient performance solution-processed organic solar cells

• Two D2-A-D1-A-D2 type tetrazine-based small molecules were synthesized.
• These molecules exhibited low LUMO and HOMO energy levels.
• Solar cells based on the synthesized molecules show Vocs as high as 0.98 V.

Two D2-A-D1-A-D2 type small molecules using Benzo[1,2-b:4,5-b′]dithiophene (BDT) as central building block, tetrazine (Tz) as an electron accepting moiety, bithiophene or terthiophene as end donor units were synthesized. The optical and electrochemical properties of synthesized molecules indicate that these molecules can absorb sunlight in a broad spectral range from 300 to 700 nm and show suitable energy level for efficient exciton dissociation. The introduction of tetrazine unit in these molecules effectively reduces the highest occupied molecular orbital (HOMO) energy levels of these molecules, thus increases air stability of these molecules as well as the open circuit voltage (Voc) in photovoltaic devices. Bulk heterojunction organic solar cells were fabricated by blending of these molecules with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) on indium tin oxide/glass substrates. This work afford promising power conversion efficiencies over 5.0%, with a large Voc of 0.98 V, measured under air mass 1.5 global irradiation of 100 mW/cm2.

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