Novel medium band gap conjugated polymers based on naphtho[1,2-c:5,6-c]bis[1,2,3]triazole for polymer solar cells

•Two new medium band gap conjugated copolymers containing naphtha[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole) were synthesized.•The resulted copolymers showed medium band gap of about 1.8 eV.•Bulk-heterojunction polymer solar cells based on copolymer P1 exhibited a moderate power conversion efficiency of 2.58%.

Two new donor-acceptor type of conjugated polymers derived from naphtho[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole) and dithieno[3,2-b:2′,3′-d]silole were prepared by Stille polymerization. The thermal, electrochemical and photophysical properties of these copolymers were studied. Both polymers have excellent thermal stability with decomposition temperature up to 430 °C. The copolymers show medium band gap of ∼1.8 eV. Inverted bulk heterojunction solar cells in which these copolymers are used as electron donors in combination with PC61BM as the electron acceptor were fabricated. Under AM 1.5 G illumination at 100 mW/cm2, device based on P1:PC61BM as the photoactive layer displays a moderate power conversion efficiency of 2.58% with an open-circuit voltage of 0.83 V, a short circuit current of 5.53 mA/cm2, and a fill factor of 56.13%. Our work indicates that naphtho[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole) can be a promising electron-deficient building block for designing donor-acceptor type of polymeric materials.

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