Fused-benzotriazole Based p-Type Polymers:Fine-tuning on Absorption Band-width and Bandgap via Backbone Thiophene and Selenophene Strategies

Four fused-benzotriazole based p-type polymers (BDT-TT, BDT-Se, BDD-TT, and BDD-Se) were designed and synthesized, and the fine-tuning on absorption band-widths and bandgaps via the backbone selenophene and thiophene strategies were reported. First, we introduced dithienothiophen[3,2-b]pyrrolobenzotriazole to co-polymerize with BDT-2F and synthesized BDT-TT. Then, we used selenophene to replace the thienothiophene units on the dithienothiophen[3,2-b]pyrrolobenzotriazole and synthesized BDT-Se. Compared to BDT-TT, BDT-Se showed a reduced bandgap from 2.0 eV to 1.89 eV. After that, we used BDD to replace BDT-2F and synthesized BDD-TT by co-polymerizing with dithienothiophen[3,2-b]pyrrolobenzotriazole. In comparison to BDT-TT, BDD-TT showed extended absorption band-width with the full-width-at-the-half-maximum (FWHM) increased from 138 nm to 229 nm and reduced bandgap from 2.0 eV to 1.71 eV. At last, we combined BDD and diselenophen[3,2-b]pyrrolobenzotriazole and synthesized BDD-Se, which achieved extended absorption and further reduced bandgap (1.61 eV). Using PC71BM as the electron acceptor material, the organic solar cells fabricated by the four polymers gave the efficiencies of 1%-2%.