An Investigation of Charge‐Transfer Processes at n ‐ TiO2 by Using a Short Laser Pulse

Abstract

The charge-transfer processes at illuminated n-TiO2 electrodes have been investigated using a nitrogen laser. The initial photopotential to the second power linearly depends on electrode potential for poly-and single-crystalline electrodes. It allows us to use photopotential measurements to determine the flatband potential. For polycrystal]ine electrodes far from the flatband potential, the characteristic time of photopotential decay (v) is determined by electric discharge through an external circuit (7 = RC). The dependence of 1/T 2 vs. E is a straight line, but the intersection with a potential axis is shifted in the cathodic direction by 0.4 V from the flatband potential. This is explained by the assumption that there is some capacitance connected in series with space-charge capacitance. From the analysis of the photopotential decay curves for a polycrystalline electrode, the rate of charge transfer from a semiconductor to an electrolyte solution was estimated to be less than 102 s -I. Near the flatband potential, the recombination photocurrent with relatively slow time decay was observed. The model which provides the explanation of these phenomena is proposed and discussed.

Current Responses to an Impulse Laser Light Illumination in Semiconductor Electrodes

“…Specifically, an initial photopotential gave information about the flatband potential, but the relaxation time gave nothing more than the external resistance. 5 In the present study, the impulse response of n-Ti02 was measured by using a current-voltage converter with a zero input resistance, which enables us to monitor the net charge-transfer process across the semiconductor-electrolyte interface. Experimental Both single-and polycrystalline Ti02 electrodes were prepared.…”