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Abstract: The interface and the related electronic properties in n-Al0.35Ga0.65N/GaN heterostructure were studied non-destructively by the spectral and transient photovoltage (PV) technique. A defect level as recombination center was observed in the buffer layer of GaN at the side close to the substrate. It was found that the GaN layer of 3 μm was completely depleted owing to the formation of two-dimensional electron gas. When the sample was illuminated at the front or the back side, with a laser radiation of 355 nm, the electron-hole pairs were generated in GaN layer and then separated there. By the action of the electric field in GaN layer, the holes moved to the substrate, while the electrons moved to the AlGaN/GaN interface. In the PV transients under the front illumination, a fast and a slow component, related to the initiative separation of the electron-hole pairs and the drift of the resultant holes, respectively, were observed. At higher illumination intensities, the bimolecular recombination happened to the fast component, while in that period of time it did not to the slow one owing to the long separation distance between the electrons and the holes. [Copyright &y& Elsevier]

Abstract: The TiO2 electrodes are fabricated with TiO2 nanoribbons and nanorods, respectively, which both match the structure of TiO2–B. The dye-sensitized solar cells made from TiO2 nanoribbon electrodes have better photoelectrical energy conversion efficiency (η) of 2.2% than those made from TiO2 nanorod electrodes, which have η of 1.8% under the xenon lamp intensity of 50 mW/cm2. The rise time and decay lifetime of the photovoltage transients are 0.37 and of 9.32 ms for the nanoribbons cells, respectively, while those are 1.39 and 6.11 ms for the nanorods cells, respectively. The reason is that only saturated Ti (IV) atoms exist in the TiO2 nanoribbons surface while there are the unsaturated coordination Ti (III) atoms in the TiO2 nanorods surface, which could trap the photo-generated electrons. So the TiO2 nanoribbons cells have better charge collection efficiency and lower interfacial charge recombination. The surface photovoltage spectra indicate that the photovoltage of the nanoribbons cells is bigger than that of the nanorods cells. [Copyright &y& Elsevier]

Abstract: Surface photovoltage spectroscopy and electric field induced surface photovoltage spectroscopy (EFISPS) were used to study the influence of the polyethylene glycol (PEG) as the binder on the electron transport in the dye-sensitized 7 μm TiO2 film electrode. The photovoltage of the TiO2 electrode prepared without PEG was higher than that of the electrode with binder, which showed that the charge transport properties of the TiO2 electrode were improved in the absence of the binder. After the electrode prepared with the binder was applied with +0.5 V voltage, three photovoltage peaks appeared at 432, 385 and 343 nm in the EFISPS, indicating that there existed impurity states in the electrode due to the carbonization of the PEG. When the TiO2 electrode prepared with binder was applied to the dye-sensitized solar cell, the photogenerated electrons from the excited dye could be trapped by these impurity states. [Copyright &y& Elsevier]

Mercurochrome-sensitized composite TiO2/SnO2 and ZnO/SnO2 photoelectrochemical cells (DSC) have been fabricated from the mixture of the SnO2 particles and the semiconductor colloid (TiO2, ZnO). The influence of the mixed ratio on the performances of the composite semiconductor photoelectrochemical cells was studied. Comparing the composite TiO2/SnO2 and ZnO/SnO2 cells with the corresponding TiO2 and ZnO cells, the incident photon-to-current conversion efficiency of the composite cells was improved greatly. The photovoltage spectra (SPS) indicated that the dye molecule was adsorbed mainly by the TiO2 and ZnO particles respectively in the composite cells. The energy barriers between the different semiconductors contributed to the improvement of the short-circuit photocurrent. The possible transport mechanism of the photogenerated electrons in composite cells was percolation through the SnO2 particles. [Copyright &y& Elsevier]