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The successful operation of a photogalvanic cell for solar energy conversion requires that the illuminated electrode should discriminate between the two redox couples in solution. In the case of the iron-thionine system the electrode must oxidize photogenerated leucothionine but not reduce the photogenerated Fe(III). Modified electrodes with coatings of thionine of up to 20 monolayers can be prepared on Pt and SnO~. These electrodes have been investigated using ring disk, cyclic voltammetry, XPES, and spectroelectrochemical measurements. Results for the modified electrode kinetics are presented for the following systems: thionine, disulfonated thionine, Fe (I ~D, Fe (CN) ~4-, Ru (bpy) ~3 +, Ce(IV), quinone, and N,N,N',N'-tetramethyl-p-phenylenediamine. The results for the Fe (III) and thionine systems show that this modified electrode is suitable for the iron-thionine photogalvanic cell.

Metal-insulator-metal cells containing metal-free phthalocyanine sandwiched between two metals (six different combinations of gold, lead and aluminium) have been prepared, and their photoelectrical properties studied in ultra-high vacuum. With irradiation incident on the non-substrate electrode the spectral response and sign of the photovoltage are consistent with conduction by injected holes. At low voltages, the photocurrent-voltage curves can be quantitatively explained by a space-charge-free theory of conduction. Energy barriers to hole injection, and hence the built-in field, arenot determined by the work function of the metal, but in each case the higher barrier occurs on the non-substrate side of the phthalocyanine. This fact, together with the observed variation of the built-in field with irradiance and the failure of the space-charge-free conduction model at high voltages, is explained by assuming that the metals make ohmic contact to the phthalocyanine and that the effective barriers to injection are determined by space-charge effects of holes trapped near the metal-insulator interface. The trap density is highest at the non-substrate side of the film and is approximately uniform with energy. The dark current exceeds the saturation photocurrent at high voltages, which suggests that the mechanism of photoinjection into the bulk is probably exciton dissociation at defects near the illuminated electrode rather than exciton-induced photoinjection directly from the metal.Reasons for the low photovoltaic power-conversion efficiencies in these cells, and theoretical limitations on more-ideal cells of this type, are discussed. * In the present paper 'photoinjection' denotes exciton-induced injection from the electrode.Lyons, L. E., and Newman, 0. M. G., Aust.

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In einer photogalvanischen Zelle für die Umwandlung von Sonnenenergie oxidiert die Elektrode (mit Thionin bedecktes Eisen) das photochemisch erzeugte Leukothionin, aber reduziert nicht das photochemisch erzeugte Fe(III).