Effect of fluorine substitution on photovoltaic properties of benzotriazole polymers

Two kinds of wide bandgap conjugated polymers, named as BDT-TTBTA and BDT-TTFBTA, were designed and synthesized based on alkylthiophene-modified benzo[1,2-b:4,5-b']dithiophene (BDT) as the donor unit, benzotriazole (BTA)/fluorobenzotriazole (FBTA) as acceptor units and alkylthiophenothiophene as pi-bridge. The thermal stability, absorption spectra, electrochemical properties and active layer morphology of these polymers were investigated to explore the impacts of F atoms on the photovoltaic performance of polymer. By introducing F atom, BDT-TTFBTA:ITIC devices obtained higher open circuit voltage (Voc) of 0.75 eV, fill factor (FF) of 48%, and short-circuit current (Jsc ) of 12.39 mA.cm (-2) than BDT-TTBTA:ITIC devices, giving rise to a higher power conversion efficiency (PCE) of 4.5% compare to BDT-TTBTA:ITIC devices.