Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 19, Issue 19, Pages 12255-12268Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c7cp01606a
Keywords
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Funding
- Science Foundation Ireland (US: Ireland Grant RENEW - Research into Emerging Nanostructured Electrodes for the Splitting of Water) [13/US/I2543]
- Science Foundation Ireland (SFI) [13/US/I2543] Funding Source: Science Foundation Ireland (SFI)
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Intentionally defect-rich zinc oxide (ZnO) nanorod-arrays were grown from solution by carefully adjusting the concentration ratio of the growth-precursors used followed by various post-deposition thermal treatments. Post-deposition rapid thermal annealing (RTA) at moderate temperatures (350 degrees C-550 degrees C) and in various atmospheres was applied to vary the defect composition of the grown nanorod-arrays. It is demonstrated that, intense, defect-related orange emission occurs solely upon RTA around 450 degrees C and is essentially independent of the atmosphere used. Extensive materials characterization was carried out in order to evaluate the origin of the orange-luminescent defects and what influence they have on the ZnO material properties. It is concluded that the oxygen vacancy-zinc interstitial defect complex (V-O-Zn-i) is responsible for the orange luminescence in the prepared materials. A kinetic formation mechanism of the V-O-Zn-i complex dependent on the RTA temperature is proposed and shown to be in accordance with the experimental findings. Furthermore it is shown that this bulk deep-level defect could act as a trap state for photo-generated electrons prolonging the charge carrier lifetime of photo-generated holes and therefore improving the charge carrier separation in the material. As a result the photo-current density under simulated sunlight is found to increase by almost 150% over as-grown samples. The potential use of this defective material in applications such as solar water splitting is outlined.
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