Fluoro-benzoselenadiazole-based low band gap polymers for high efficiency organic solar cells

Low band gap polymers are of great interest for future applications in solar cells. By using monofluoro-2,1,3-benzoselenadiazole (FBSe) as the electron acceptor and benzodithiophene (BDT) or indacenodithiophene (IDT) as the electron donor, two novel FBSe-based polymers, PBDT-T-FBSe and PIDT-T-FBSe, were synthesized via a microwave-assisted palladium-catalyzed Stille polymerization. Both of the polymers exhibited broad absorption and lower highest occupied molecular orbital (HOMO) energy levels, which contribute to the high short current density (Jsc) and open circuit voltage (Voc). Higher power conversion efficiencies of 5.00% for PBDT-T-FBSe and 4.65% for PIDT-T-FBSe were achieved in a bulk heterojunction (BHJ) photovoltaic device with a configuration of ITO/PEDOT:PSS/polymer:PC71BM/bis-C60/Ag under the illumination of AM1.5G at 100 mA cm−2. These results demonstrate the importance of FBSe as an electron-deficient unit in the design of donor–acceptor photovoltaic polymers.