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Barriers for interfacial back-electron transfer: A comparison between TiO2 and SnO2/TiO2 core/shell structures.
Ludovic Troian-Gautier1, Renato N Sampaio1, Eric J Piechota1
1Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
Investigating back-electron transfer (BET) kinetics in TiO2 and SnO2/TiO2 nanoparticles reveals higher activation energies for core-shell structures. A trap state model explains the increased energy barrier, impacting dye-sensitized solar cell efficiency.
Area of Science:
- Materials Science
- Photochemistry
- Nanotechnology
Background:
- Back-electron transfer (BET) is a critical process in dye-sensitized solar cells (DSSCs).
- Understanding the kinetics of BET is essential for optimizing DSSC performance.
- TiO2 and SnO2/TiO2 core-shell nanoparticles are promising photoanode materials.
Purpose of the Study:
- To investigate the temperature-dependent kinetics of BET from TiO2 and SnO2/TiO2 core-shell nanoparticles.
- To compare BET kinetics with different donor-bridge-acceptor (D-B-A) sensitizers.
- To elucidate the factors influencing the activation energy barrier in these systems.
Main Methods:
- Temperature-dependent kinetic measurements over a 110°C range.
- Utilized two D-B-A sensitizers with varying bridging ligands (phenyl vs. xylyl).
- Arrhenius analysis to determine activation energies (Ea).
Main Results:
- Significantly larger activation energies for core-shell oxides (Ea = 32 ± 4 kJ/mol) compared to TiO2 alone (Ea = 22 ± 6 kJ/mol).
- First quantification of BET kinetics for SnO2/TiO2 core-shell materials.
- A low-energy trap state model involving the TiO2 rutile shell was preferred to explain the increased barrier.
Conclusions:
- Core-shell SnO2/TiO2 nanoparticles exhibit a higher activation energy barrier for BET compared to TiO2.
- The findings suggest that trap states in the TiO2 shell play a crucial role in recombination.
- Kinetic analysis provided rate constants for intramolecular equilibrium, showing a smaller free energy change for adiabatic transfer.
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