Effect of π-bridge groups based on indeno[1,2-b]thiophene D-A-π-A sensitizers on the performance of dye-sensitized solar cells and photocatalytic hydrogen evolution

Donor-acceptor-pi-acceptor (D-A-pi-A) organic dyes are promising candidates for efficient dye-sensitized solar cells (DSCs) and photocatalytic H-2 evolution due to their high range of visible-light response and strong light-capturing capabilities. However, the low charge transfer rate and severe charge recombination at the interface still limit their photovoltaic performance and photocatalytic activities. In this work, three indeno[1,2-b]thiophene-based sensitizers (SD1, SD2 and SD3) with a 2,3-diphenylquinoxaline (QT) auxiliary acceptor and cyclopentadithiophene (CPDT)-benzene/thiophene/furan different pi-bridge moieties have been synthesized and applied in DSCs and photocatalytic H-2 production to investigate the effect of the pi-bridge moiety on the photovoltaic performance and photocatalytic activities. Optical/electrochemical data and density functional theory (DFT) calculations clearly showed that the introduction of a benzene pi-bridge in SD1 resulted in a large torsional angle between CPDT and benzene, and then inhibited dye aggregation and charge recombination. Therefore SD1-based DSCs exhibited the highest power conversion efficiency (PCE) of 8.96% under one sun illumination. In addition, among the three sensitizers, the SD2 containing thiophene pi-bridge unit exhibited the best hydrophilicity and planarity with a torsional angle <1 degrees, which greatly improved the charge transfer process at the solution/dye/TiO2 interface and dye regeneration. Thus, a remarkable H-2 evolution rate of 23.5 mmol g(-1) h(-1) was obtained over the SD2@Pt/TiO2 photocatalyst.