Abstract
A novel metal-free quinoxaline-based molecular framework with a dual donor and dual acceptor (DD-π-AA) motif has been introduced. Four sensitizers (AP6, AP8, AP9, and AP12) have been synthesized and fully characterized via UV–Vis absorption, cyclic voltammetry, density functional theory (DFT) calculations, time-correlated single photon counting (TCSPC), and in dye-sensitized solar cell (DSC) devices. Structural modifications to both the donor and acceptor/anchor regions were evaluated via structure–property relationships without altering the quinoxaline π-bridge. Through careful dye design, a broadly absorbing near-infrared (NIR) sensitizer extending electricity production to 800 nm is realized in DSC devices. Ground- and excited-state oxidation potentials were measured to show energetically favorable charge transfer events. Importantly, the dye structure was found to have a strong influence on dye energetics in different environments with structural elements allowing for either similar or dramatically different solution versus film measurements. The DSC device electrolyte was also found to have a significant influence on dye energetics as well. Electron transfer events were probed for each dye with DSC device measurements and with TCSPC studies. The results are correlated to the dye structures.
Highlights
Dye-sensitized solar cells (DSCs) remain a promising and intensely studied area of research after two decades of exploration [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
The effect of structural modifications was studied via UV–Vis absorption spectroscopy, electrochemical analysis, computational density functional theory (DFT) analysis, time-correlated single photon counting (TCSPC) spectroscopy, and DSC device analysis
The evaluation of the dye energetics on film showed that the dye anchor spacing plays a critical role in the validity of using solution measurements to approximate dye–TiO2 film energetics
Summary
Dye-sensitized solar cells (DSCs) remain a promising and intensely studied area of research after two decades of exploration [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. In typical n-type DSC devices, dye molecules are first photoexcited followed by the transfer of electrons to the conduction band (CB) of TiO2. The dye is one of the most important components of DSC devices for determining which photon energies are useable. Broad UV–Vis–near-infrared (NIR) absorption properties are crucial for realizing the highest efficiency DSC devices possible [16]. A DSC device employing organic dyes surpassing 14% power conversion efficiency (PCE) has been reported owing to well-positioned energy levels, high extinction coefficients, and strong binding properties [17]. In order to further improve DSC device performances, dyes with NIR absorption (>750 nm) are required.
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