Experiments on Dye Sensitization of Zinc Oxide

Abstract

By means of two experimental techniques, the sensitization of the conductivity and the discharge both of ZnO single crystals and zinc oxide-resin layers with rhodamin B, eosin, and methylene blue have been studied. Stimulated by current-voltage and capacitance measurements with ZnO single crystals in a suitable electrochemical cell, the sensitization was investigated of anodically polarized ZnO crystals by dyes soluted in the electrolyte of the electrochemical cell: + In || ZnO single crystal || electrolyte + dye || platinum -. A strong increase of the anodic current was obtained by illumination with the corresponding light through the crystal from the backside. In addition to the photovoltage, the photocurrent of the anodically polarized ZnO was measured as a function of the dye concentration in the electrolyte at a constant voltage (2 V). To get more information on the mechanism, these experiments were completed by discharge measurements both of ZnO-resin layers and ZnO single crystals charged under a corona with a dc voltage. The dyed zinc oxide was illuminated under similar conditions. At approximately the same surface concentration of the corresponding dye (as mentioned for the electrochemical experiments) and at the same flux of photons, the decay of the surface potential both of ZnO single crystal and a ZnO-resin layer with the time was measured under illumination with light of various wavelengths. Some experiments on the influence of a second dye in the electrolyte on the extent of sensitization by the first dye are discussed.

New Experiments on the Sensitization of Zinc Oxide by Means of the Electrochemical Cell Technique

“…The precise proportionality of the photocurrent to the light intensity recognized in former investigations (15,20) could be confirmed by the independence of the formal quantum yield from the light intensity, as may be seen from Fig. 3.…”

“…The sensitizing behaviors of Rhodamine B, Rose Bengale, Eosin, Fluorescein, and Methylene Blue have been studied by means of current-voltage curves in the above-mentioned electrochemical cell in the dark and under illumination (17)(18)(19)(20). In this paper, the sensitizing ability only of Rhodamine B is dealt with in more detail.…”

On the Influence of Sensitization of the Electron Transfer Through the Interface Zinc Oxide/Electrolyte by Salt Additions

“…The kinetics of the formation and the decay of the encounter complex DQ, as well as of the excited singlet, read [15] Substituting and rearranging Eq. [13], [14], and [15] Icos A linear function should be obtained if the reciprocal cosensitized photocurrent 1//cos will be plotted vs. the reciprocal value of the quencher concentration 1/[Q-] ----1/CNaX. This correlation is represented in Fig.…”

“…Then they were exposed to light of a defined photon flux and wavelength in a closed chamber with a revolving plate and a translucent probe for potential measurements. The exact experimental details have been published (15).…”