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

Abstract

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 (J_sc) and open circuit voltage (V_oc). 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.