Effect of fluorination on n-type conjugated polymers for all-polymer solar cells

Abstract

Four naphthalene diimide (NDI) based donor–acceptor conjugated polymers for using in all-polymer organic solar cells were synthesized and characterized. The effect of inclusion of a different number of fluorine atoms on the donor portion of the polymer was thoroughly investigated via a range of techniques. Fluorination of the polymer backbone lowered both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) and simultaneously broadened the energy bandgap of the polymer. Incorporation of a different number of fluorine atoms on the donor portion of the polymer significantly affected the solar cells' power conversion efficiency from 0.67% to 2.50%. The “fluorine” effect suggests fluorine substitution should be considered for achieving high performance PSCs in the future design of new materials.