The “formal quantum yield” of the sensitization of the anodic photocurrent of zinc oxide by Rhodamine B has been determined by means of an electrochemical cell technique. Zinc oxide was used as a single crystal in the electrochemical cell +normalIndium|normalZnO crystal|normalElectrolyte+normalDye|normalPlatinum− in aqueous and methanol electrolytes. Simultaneously, the adsorption of the dye on zinc oxide powder has been measured. The influence of the solvent on the extent of the adsorption is significant. The important role of the cosensitizer on the sensitizing ability of the dye is discussed.

No 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.

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.

An Hand von Strom‐Spannungs‐Kurven im Dunkeln und unter Einstrahlung von 365‐nm‐Licht an der KetteMetall | ZnO‐Einkristall | Elektrolyt | Ptwurde der Durchtritt von Elektronen und Ionen durch die Phasengrenze ZnO/Elektrolyt ermittelt. Auf Grund des anodischen Teils der Strom‐Spannungs‐Kurven im Dunkeln und unter Licht darf geschlossen werden, daß ein Übergang von Elektronen vom Elektrolyten ins Leitungsband des Zinkoxids nicht ohne weiteres möglich ist. Im Dunkeln können leicht Elektronen aus dem Leitungsband in den Elektrolyten treten. Bei Lichteinwirkung hingegen tritt eine Rekombination der Defektelektronen der Elektron‐Lochpaare mit den von den Sauerstoffionen bzw. den Elektrolytionen abgebbaren Elektronen ein. Die von den Elektron‐Lochpaaren stammenden zurückbleibenden Elektronen fließen nunmehr als freie Ladungsträger zur positiv polarisierten Elektrode ab. In Gegenwart von Chinhydron im Elektrolyten wird grundsätzlich am Mechanismus nichts geändert.Infolge dieser elektronischen Umladungsreaktion und der hierdurch verursachten Desorption des Sauerstoffs können die überschüssigen Zn2+‐Ionen in den Elektrolyten übertreten. Bei Fehlen geeigneter Redoxsysteme, die eine Sauerstoffumladung verhindern, kommt es zu einem Ausbau von ZnO, der in sauren Bereichen (pH = 3 bis 4) in Form hexagonaler Löcher auftritt, wenn man die (0001)‐Fläche des Einkristalls mit dem Elektrolyten in Berührung bringt.Aus den Kapazitätsmessungen sowohl im Dunkeln als auch unter Licht kann geschlossen werden, daß praktisch der gesamte Spannungsabfall in der Verarmungsrandschicht des Zinkoxids in der Nähe der Phasengrenze ZnO/Elektrolyt liegt.