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

Abstract

Donor–acceptor–π–acceptor (D–A–π–A) organic dyes are promising candidates for efficient dye-sensitized solar cells (DSCs) and photocatalytic H₂ 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 π-bridge moieties have been synthesized and applied in DSCs and photocatalytic H₂ production to investigate the effect of the π-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 π-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 π-bridge unit exhibited the best hydrophilicity and planarity with a torsional angle <1°, which greatly improved the charge transfer process at the solution/dye/TiO₂ interface and dye regeneration. Thus, a remarkable H₂ evolution rate of 23.5 mmol g⁻¹ h⁻¹ was obtained over the SD2@Pt/TiO₂ photocatalyst.