Photorechargeability and charge transfer characteristics in titanium oxide photocatalytic films with selforganized nano structure

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The photorechargeable battery is a new solar device that converts photon energy to electrochemical energy and stores it in situ in a single cell. Since any external electrical circuits are not necessary for the charge, the application to separated small auxiliary batteries is expected. However, because of the upper limit of the photo-emf, realization of an efficient photocharge is a problem to be solved.In this research, low energy storage sites were created on the surface of titanium oxide thin films with self-organized nano-structure by the reduction with hydrogen plasma and photo-electrochemical etching. The photo-emf and the photorechargeable quantity reduced in the films when oxygen defects were produced on the surface by the etching, while they showed a rapid increase when the etching was not associated with oxygen defects. If porous films are treated with the same manner, synergistic effect is expected for the photorechargeablity.Next, the control of the crystal growth was attempted for whisker-shaped thin films by an external electric field and UV light in chemical vapor deposition. An increase of efficiency was expected by the exposure of the sites with high photo activity on the crystal surface with self-organized nano-structure. The change in the crystal growth was observed with the external excitation, while the effect on the photorechargeability was small. Further research with high external excitation is in progress.