Donor–acceptor dyes incorporating a stable dibenzosilole π-conjugated spacer for dye-sensitized solar cells

Abstract

Four novel organic dyes including three based on dibenzosilole (YS01–03) and one based on fluorene (YS04) were synthesized, and their photophysical properties and dye-sensitized solar cell (DSC) performances were characterized. The silicon-containing dibenzosilole-based dyes (YS01–03) were superior to the carbon analogue fluorene-based dye YS04 in incident-photon-to-current conversion efficiency (IPCE), and total solar-to-electric conversion efficiency (η), with YS03, which has the bulkiest and most branched electron donor group, achieving the highest η of 5.07% compared to 2.88% of YS04. To better understand how silicon influences the excited state oxidation potentials (S^+/*) and absorption maxima (λ_max), the equilibrium molecular geometries of dyes YS01–04 were calculated using density functional theory (DFT) utilizing B3LYP energy functional and DGDZVP basis set. It was shown that the torsion angles (θ1 and θ2) across the biphenyl linkages of dyes containing silicon (YS01–03) were less twisted than that of the silicon-free dye (YS04), which enhanced the π–π* overlap, and that translated into photocurrent enhancements in the silicon-containing dyes YS01–03. Moreover, the vertical electronic excitations and S^+/* of dyes YS01–04 were studied using different long-range corrected time-dependent DFT methods, including CAM-B3LYP, LC-BLYP, WB97XD, and LC-wPBE at the basis set level DGDZVP. Excellent agreement between the calculated, using CAM-B3LYP/DGDZVP, and experimental results was found.