Benzodithiophene-based two-dimensional polymers with extended conjugated thienyltriphenylamine substituents for high-efficiency polymer solar cells

Two novel donor-acceptor (D-A)-type two-dimensional (2-D) polymers of PTTPABDT-DTBT and PTTPABDT-DFDTBT were synthesized and characterized, in which extended conjugated side chained 4-thienyltriphenylamine benzo[1,2-b:4,5-b′]dithiophene (TTPABDT) as the donor unit, thiophene (T) as the π-bridge, benzo[c][1,2,5]thiadiazole (BT) and 5,6-difluorobenzo[c][1,2,5]thiadiazole (DFBT) as the acceptor units. Due to the introduction of the extended conjugated side chained TTPA, polymers exhibited good thermal stabilities, broad absorption spectra and narrow optical band gaps. The hole mobility of 2.15 × 10^-4 cm² V^-1 s^-1 was obtained in the PTTPABDT-DFDTBT/PC₇₁BM blended film, which is two times higher than that of the PTTPABDT-DTBT/PC₇₁BM blended film. Finally, the PTTPABDT-DFDTBT/PC₇₁BM-based polymer solar cells presented the best power conversion efficiency (PCE) of 4.29% with a fill factor (FF) of 62.5%, while PTTPABDT-DTBT-based devices shown a PCE of 3.92% with a FF of 58.8%. The results indicate that the introduction of the extended conjugated TTPA side chain into the D-A-type 2-D polymers is an efficient approach to improve photovoltaic performances for its resulting polymers.