Investigating interfacial electron transfer in dye-sensitized NiO using vibrational spectroscopy
Fiona A Black1, Charlotte A Clark2, Gareth H Summers3
1School of Chemistry, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK. elizabeth.gibson@newcastle.ac.uk.
Physical Chemistry Chemical Physics : PCCP
|March 7, 2017
Summary
Time-resolved infrared spectroscopy reveals that dye 1 forms efficient charge-separated states on NiO, outperforming dye 2. This difference in charge-transfer dynamics explains their varying performance in photoelectrochemical devices.
Area of Science:
- Materials Science
- Photochemistry
- Spectroscopy
Background:
- Understanding charge-separated states is crucial for photoelectrochemical devices.
- Organic donor-π-acceptor dyes on metal oxides are key components.
- P-type metal oxides like NiO are less understood than n-type materials in dye interactions.
Purpose of the Study:
- To investigate the structure and lifetime of excited states in organic dyes adsorbed on NiO.
- To compare charge-transfer dynamics between two structurally similar dyes with different acceptors (maleonitrile vs. bodipy).
- To correlate excited-state behavior with device performance in photoelectrochemical applications.
Main Methods:
- Time-resolved infrared absorption spectroscopy (TRIR) was employed.
- Two donor-π-acceptor dyes (triphenylamine-thiophene with maleonitrile or bodipy acceptors) were studied.
- Spectroscopic analysis was performed in solution and adsorbed on NiO, with and without electrolyte.
Main Results:
- Dye 1 (maleonitrile acceptor) exhibited rapid (<1 ps) and efficient charge-transfer from NiO, forming stable charge-separated states.
- Dye 2 (bodipy acceptor) showed slower charge transfer and the presence of multiple excited species, indicating electronic decoupling.
- The charge-transfer excited state in dye 2 had a short lifetime (τ ≈ 30 ps) on NiO, suggesting less efficient charge separation.
Conclusions:
- Dye 1's superior performance is attributed to its efficient and rapid charge separation on NiO.
- Dye 2's limitations stem from slower charge transfer and potential electronic decoupling within the molecule.
- Fast charge recombination is a significant challenge for p-type metal oxide-based photocathodes and Z-scheme photocatalysis.
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