Improved Photovoltaic Performance of a Side‐Chain D–A Polymer in Polymer Solar Cells by Shortening the Phenyl Spacer between the D and A Units

To study the influence of the spacer between the donor (D) and acceptor (A) units in a side chain on the photophysical and photovoltaic performance, a novel side‐chain D–A conjugated copolymer of PDPAT‐BDT‐BT is made, which contains binary donor units of N , N ‐diphenyl­thiophen‐2‐amine (DPAT) and benzo[1,2‐b:4,5‐b′]dithiophene (BDT) in the main chain and an appending benzothiadiazole (BT) acceptor unit in the side chain. Compared with its counterpart of PDPAT‐BDT‐BT, which has an additional phenyl spacer between the DPAT and BT units, this PDPAT‐BDT‐BT exhibits a smaller optical bandgap, a broader absorption range, and a lower highest occupied molecular orbital (HOMO) energy level (−5.42 eV), as well as improved photovoltaic properties in bulk heterojunction polymer solar cells containing [6,6]‐phenyl‐C 71 ‐butyric acid methyl ester as an electron acceptor. A maximum power conversion efficiency of 3.27% with an open circuit voltage of 0.87 V and a fill factor of 49.8% are obtained in the cells. This work indicates that the photophysical and photovoltaic performance of the side‐chain D–A polymers in polymer solar cells can be significantly improved by shortening the phenyl spacer between the D and A units.