Increasing thiophene spacers between thieno[3,2-b]thiophene and benzothiadiazole units in backbone to enhance photovoltaic performance for their 2-D polymers

•Two-dimensional polymers with thieno[3,2-b]thiophene-benzothiadiazole main-chain were designed.•The photovoltaic performance of both polymers in solar cells was studied.•The polymer with the greater number thiophene spacers exhibited higher PCE and Jsc in the backbone.

In order to investigate the effect of thiophene spacers in backbone between electron-rich thieno[3,2-b]thiophene (TT) and electron-deficient benzothiadiazole (BT) units on the photovoltaic properties, novel two-dimensional (2-D) polymers with appending conjugated dioctylthiophene units in the 3,6-positions of TT were designed and synthesized, in which one or two thiophene spacers were embedded between TT and BT, respectively. The polymer with two thiophene spacers exhibited a broader absorption and higher power conversion efficiency in the bulk hetero-junction polymer solar cells. The best performance with efficiency up to 3.34% and short-circuit current values of 12.6 mA/cm2 was obtained, which are 2.1 and 3.0 times higher than those corresponding values for the polymer with only one thiophene spacer. Our work indicates that increasing the numbers of thiophene spacers between TT and BT moieties in the backbone is an efficient method to enhance the photovoltaic performance of their 2-D polymers in polymer solar cells.

Graphical abstractNovel two dimensional (2-D) conjugated polymers P1 and P2 were synthesized, in which one and two thiophene spacers were embedded between the thieno[3,2-b]thiophene and benzothiadiazole units in the main chain, respectively. Effect of thiophene spacers on photovoltaic performance of the resulted copolymer was well investigated in the bulk heterojunction polymer solar cells. The maximum PCE of 3.34% and Jsc of 12.6 mA/cm2 were obtained in the P2/PC61BM-based devices, which are 2.1 and 3.0 times higher than those corresponding values in the P1/PC61BM-based devices.Figure optionsDownload full-size imageDownload as PowerPoint slide