The effect of fluorination on the photovoltaic performance of the D–A copolymers containing naphtho[2,3-c]thiophene-4,9-dione and bithiophene moieties

Four D–A copolymers, PNTDBT, PFNTDBT, PNTDFBT and PFNTDFBT, were prepared for systematically studying the effect of fluorination on photovoltaic performance. The fluorinated copolymers, PFNTDBT, PNTDFBT and PFNTDFBT, gave higher FF (∼70%) than PNTDBT due to their reduced bimolecular recombination and balanced mobilities. PNTDFBT with F on the BT unit shows a higher mobility than that of PFNTDBT with F on the NTD unit, leading to a higher J_sc. PFNTDFBT gave the highest PCE, 7.79%, which might result from its higher mobility and the optimal miscibility between PFNTDFBT and PC₇₁BM.