Ultrafast Electron Injection Dynamics of Photoanodes for Water-Splitting Dye-Sensitized Photoelectrochemical Cells

Abstract

Efficient conversion of solar energy into useful chemical fuels is a major scientific challenge. Water-splitting dye-sensitized photoelectrochemical cells (WS-DSPECs) utilize mesoporous oxide supports sensitized with molecular dyes and catalysts to drive the water-splitting reaction. Despite a growing body of work, the overall efficiencies of WS-DSPECs remain low, in large part because of poor electron injection into the conduction band of the oxide support. In this study, we characterize the ultrafast injection dynamics of several proposed oxide supports (TiO2, TiO2/Al2O3, SnO2, SnO2/TiO2) under identical conditions using time-resolved terahertz spectroscopy. In the absence of an Al2O3 overlayer, we observe a two-step injection from the dye singlet state into nonmobile surface traps, which then relax into the oxide conduction band. We also find that, in SnO2-core/TiO2-shell configurations, electron injection into TiO2 trap states occurs rapidly, followed by trapped electrons being released into SnO2 on the hundreds of picoseconds time scale.

Proton-Induced Trap States, Injection and Recombination Dynamics in Water-Splitting Dye-Sensitized Photoelectrochemical Cells

“…42 The TRTS scans shown in Figure 4 agree with this picture, with mobile electrons Recombination from the semiconductor occurs in the μs to ms range. In Ru-EtOH electrodes, trapped electrons persist for tens of nanoseconds before thermalizing and diffusing via a trapping/ detrapping random walk process.…”

Boosting the photocatalytic H2 evolution activity of Fe2O3 polymorphs (α-, γ- and β-Fe2O3) by fullerene [C60]-modification and dye-sensitization under visible light irradiation

“…[28][29][30] Recently, Schmuttenmaer et al proposed that the overall efficiencies of water-splitting dye-sensitized photoelectron chemical cells (WS-DSPECs) remain low in large part because of poor electron injection into the conduction band (CB) of the oxide support. 31 The electrons transfer from the LUMO of the dye to the CB of the oxide support. The dye's HOMO must be more positive than the sacricial reagent's redox potential and its LUMO must be more negative than the semiconductor's CB.…”

Applicability of the thin-film approximation in terahertz photoconductivity measurements

“…One feasible option is found in water-splitting dye sensitized photoelectrochemical cells (WS-DSPECs) that use solar energy to renewably produce chemical fuels. [1][2][3][4][5][6] A critical component of WS-DSPECs is the photoanode material, which consists of a wide bandgap metal oxide material that has a photoabsorbing dye attached to its surface. In the dark, the metal oxide material is an insulator, yet when the dye molecule is photoexcited, it can transfer its excited state electron into the conduction band of the metal oxide material.…”

“…In the dark, the metal oxide material is an insulator, yet when the dye molecule is photoexcited, it can transfer its excited state electron into the conduction band of the metal oxide material. 4,7 The metal oxide allows the transport of the photogenerated charges, which travel through the porous nanoparticulate metal oxide film until being transported to a dark cathode to facilitate a proton reduction reaction to generate H 2 . Understanding this transport mechanism, and in particular, carrier mobility and lifetime, is crucial for the optimization of WS-DSPECs.…”

“…These samples were prepared following previously published techniques, 15,16 and a screen-printed paste of SnO 2 was prepared as described previously. 3,4,10 The deposition of the layer and sensitization was repeated one, three, and five times, resulting in a total layer thickness of 3.3 mm 6 0.3 mm, 8.2 mm 6 0.3 mm, and 12.6 mm 6 1.0 mm, respectively.…”