Synthesis, characterization and device optimisation of new poly(benzo[1,2-b:4,5-b′]dithiophene-alt-thieno[3,4-d]thiazole) derivatives for solar cell applications

New alternating copolymers based on benzo[1,2- b :4,5- b ′]dithiophene and thieno[3,4- d ]thiazole derivatives have been synthesized by using different combinations of side chains and spacers in order to study their effect on the optical, electrochemical and photovoltaic properties. Optical and electrochemical characterization were performed and the resulting copolymers exhibit optical bandgaps ranging from 1.66 to 1.80 eV, HOMO energy levels between −5.19 and −5.30 eV and LUMO energy levels between −3.60 and −3.72 eV. Photovoltaic devices were fabricated and characterized after a careful optimization of the active layer fabrication by using different solvents, additives and acceptors. Following this process, PCEs up to 4.4% were obtained.