Ultrafast recombination dynamics in dye-sensitized SnO2/TiO2 core/shell films
In dye-sensitized photoelectrosynthesis cells (DSPECs), molecular chromophores and catalysts are integrated on a semiconductor surface to perform water oxidation or CO2 reduction after a series of light-induced electron transfer events. Unfortunately, recombination of the charge separated state (CSS) is competitive with productive catalysis. To overcome this major obstacle, implementation of photoanodic core/shell films within these devices improve electrochemical behavior and slow recombination through the introduction of an energetic barrier between the semiconductor core and oxidized species on the surface. In this study, interfacial dynamics are investigated in SnO2/TiO2 core/shell films derivatized with a Ru(II)-polypyridyl chromophore ([RuII(bpy)2(4,4'-(PO3H2)2bpy)]2+, RuP) using transient absorption methods. Electron injection from the chromophore into the TiO2 shell occurs within a few picoseconds after photoexcitation. Loss of the oxidized dye through recombination occurs across time scales spanning 10 orders of magnitude. The majority (60%) of charge recombination events occur shortly after injection (τ = 220 ps), while a small fraction (≤20%) of the oxidized chromophores persists for milliseconds. The lifetime of long-lived CSS depends exponentially on shell thickness, suggesting that the injected electrons reside in the SnO2 core and must tunnel through the TiO2 shell to recombine with oxidized dyes. While the core/shell architecture extends the lifetime in a small fraction of the CSS, making water oxidation possible, the subnanosecond recombination process has profound implications for the overall efficiencies of DSPECs.
- Research Organization:
- University of North Carolina, Chapel Hill, NC (United States); Energy Frontier Research Centers (EFRC) (United States). Center for Solar Fuels (UNC EFRC)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- SC0001011
- OSTI ID:
- 1335127
- Journal Information:
- Journal of Physical Chemistry Letters, Vol. 7; ISSN 1948-7185
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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