Y. Mirovsky’s research while affiliated with Weizmann Institute of Science and other places

Bei Culnsz-Proben mit geringem Energieumwandlungswirkungsgrad (2%) wird eine relativ heterogene Oberfläche gefunden, die teilweise stark mit In angereichert ist.

Es werden unterschiedliche Oberflächenbehandlungen an den Titel-Photoelektroden durchgeführt, wie z.B. Cd-Dotierung, chemisches Ätzen, milde Luftoxidation, die zeigen, daß diese Chalkogenide äußerst sensitiv gegenüber solchen Oberflächenveränderungen sind.

The photoelectrochemical properties of the ternary semiconductor CdIn//2Se//4 is further investigated. Photoelectrochemical etching increases the photocurrent of this material by an order of magnitude in various electrolytes. Cyclic voltammetry, Auger analyses, and thermodynamic calculations suggest that oxide is unlikely to be produced during photoetching. Degradation of the photocurrent with time in polysulfide electrolyte due to photocorrosion is studied with x-ray photoelectron spectroscopy (XPS). Thermodynamic and solid-state data are used for the construction of the band diagram of CdIn//2Se//4/polysulfide system. It is shown that the time behavior of this system resembles that of CdSe/polysulfide photoelectrochemical cell.

Using recently determined thermodynamic data for CuInS2 and CuInSe2, we estimated the Gibbs free energy changes for several decomposition and exchange reactions for these semiconductors in aqueous polysulfide and aqueous polyiodide, and, where possible, calculated their corresponding electrode potentials. Exchange reactions for In2O3, believed to be the native oxide on these semiconductors, are included, as well as chemical conversion reactions for their preparation from the corresponding indium sesquichalcogenides. With the aid of measured flat-band potentials, the band edges of the semiconductors (or semiconductor/surface oxide systems) are determined on the electrochemical scale and the quasi-Fermi levels are estimated from literature data. When these are combined with the calculated decomposition potentials and the measured redox potentials, (in)stability electron energy diagrams that are strictly valid only near open circuit are constructed. On the basis of these the absence of Se/S exchange on n-CuInSe2 in polysulfide, the protective function of an indium oxide surface layer on CuInSe2 in polyiodide, the stabilizing effect, on CuInSe2, of adding copper ions to polyiodide solutions, and the stability of CuInSe2 against reductive decomposition can be understood. Also, the greater likelihood of In2X3 (X = S or Se) formation (in polysulfide) on CuInS2 than on CuInSe2, the possibility of CuInSe2 formation on the surface of In2Se3, immersed in Cu-containing solutions, and the photoanodic decomposition of n-CuInSe2 under illumination in acetonitrile can be rationalized. The data do not explain the difference between CdSe and CuInSe2, with respect to chemical Se/S exchange, the absence of InI3 formation in In2O3 in polyiodide, the absence of photoanodic decomposition of CuInX2 into copper and indium sulfides in polysulfide, and the lack of Cu2Se formation from photoanodic decomposition of CuInSe2 in polyiodide. In these latter cases kinetic factors, which may be related to the large number of reactants and charge carriers that are involved in some of the suggested decomposition reactions, appear to be dominant. Because of the possibility of very large deviations from steady state and the occurrence, at least initially, of products in states very different from their standard state, the free energy changes for virtually all decomposition reactions are expected to be shifted sufficiently to make these and other semiconductors thermodynamically unstable toward initial decomposition.

The photoelectrochemistry of and in polysulfide electrolyte is studied with particular emphasis on the pretreatments of the electrodes and on their output stability. The use of Cd doping, (photoelectro)chemical etching, and mild air oxidation all were found to improve electrode performance. The effect of air oxidation was reproducible only for the diselenide, where it improved the fill factor and, because of a negative shift of the flatband potential, the open‐circuit voltage. Optimized cells showed, at elevated temperatures, conversion efficiencies around 5 and 7.5% for the sulfide and selenide, respectively. The positive temperature dependence of the photo‐I‐V characteristics at both low and high illumination intensities, the existence of optimal polysulfide solution compositions, the linear dependence of the photocurrent on the light intensity, and the effects of temperature, solution composition, and initial current density on the photocurrent decrease during the first minute of operation of the cells, are ascribed to limitations of the charge‐transfer process across the solid/liquid interface. Thermally activated rates of ad‐ and desorption of sulfur containing solution species on the semiconductor surface and/or the presence of adsorption‐induced electronic states in the bandgap are postulated as causes for this behavior. Notwithstanding these limitations the cells are resistant to photocorrosion, after the initial decrease is arrested, in contrast to what is known for similar Cd‐chalcogenide‐based systems. We suggest that this stability, which persists under load and at high light intensities, is due to the strength and character of the bonds in , or to the presence of a top layer of indium oxide in which recombination will take place, or to both.

The photoelectrochemistry of n-CuInS/sub 2/ and CuInSe/sub 2/ in polysulfide electrolyte is studied with particular emphasis on the pretreatments of the electrodes and on their output stability. The use of Cd doping, (photoelectro) chemical etching, and mild air oxidation all were found to improve electrode performance. The effect of air oxidation was reproducible only for the diselenide, where it improved the fill factor and, because of a negative shift of the flatband potential, the open-circuit voltage. Optimized cells showed, at elevated temperatures, conversion efficiencie around 5 and 7.5% for the sulfide and selenide, respectively. The positive temperature dependence of the photo-I-V characteristics at both low and high illumination intensities, the existence of optimal polysulfide solution compositions, the linear dependence of the photocurrent on the light intensity, and the effects of temperature, solution composition, and initial current density on the photocurrent decrease during the first minute of operation of the cells, are ascribed to limitations of the charge-transfer process across the solid/liquid interface. Thermally activated rates of ad- and desorption of sulfur containing solution species on the semiconductor surface and/or the presence of adsorption-induced electronic states in the bandgap are postulated as causes for this behavior. Notwithstanding these limitations the cells ar resistant to photocorrosion, after the initial decrease is arrested, in contrast to what is known for similar Cd-chalcogenide-based systems. We suggest that this stability, which persists under load and at high light intensities, is due to the strength and character of the bonds in CuIn-dichalcogenides, or to the presence of a top layer of indium oxide in which recombination will take place, or to both.

n-CuInSâ and n-CuInSeâ were subjected to surface analyses by x-ray photoelectron and Auger electron spectroscopy, after their use as photoanodes in polysulfide solutions. For CuInSâ samples that had a poor (ca. 2%) conversion efficiency, a rather heterogeneous surface was found, with patches rich in In, which is probably present mainly as oxide. Some CuO was found as well, although the top layer was depleted in Cu, compared to a reference sample. More efficient (ca. 5%) samples showed a more homogeneous surface and even stronger Cu depletion. These changes are ascribed to additional surface treatments, viz., dipping in hot KCN solution and thermal oxidation o the resultant etched surface. For CuInSeâ samples, no significant exchange of lattice Se by S from the polysulfide solution is seen, in sharp contrast to what is observed for CdSe or CdInâSeâ. If sulfur is found, its presence could be correlated with the spurious occurrence of Cd (used as dopant) or Ag (used for the ohmic back contact). Cu depletion also occur near the surface of the diselenide after use in polysulfide solution. Most of the remaining In seems to occur in indiu oxide and/or indium selenide. Cuâ was found neither here nor on the surface of the more efficient disulfide sample. It is suggested that the occurrence of an indium oxide top layer, aided by thermal oxidation of the electrode in the case o CuInSeâ, has a beneficial effect on electrode performance.

The photoelectrochemistry of n-CuInSâ and CuInSeâ in polysulfide electrolyte is studied with particular emphasis on the pretreatments of the electrodes and on their output stability. The use of Cd doping, (photoelectro) chemical etching, and mild air oxidation all were found to improve electrode performance. The effect of air oxidation was reproducible only for the diselenide, where it improved the fill factor and, because of a negative shift of the flatband potential, the open-circuit voltage. Optimized cells showed, at elevated temperatures, conversion efficiencie around 5 and 7.5% for the sulfide and selenide, respectively. The positive temperature dependence of the photo-I-V characteristics at both low and high illumination intensities, the existence of optimal polysulfide solution compositions, the linear dependence of the photocurrent on the light intensity, and the effects of temperature, solution composition, and initial current density on the photocurrent decrease during the first minute of operation of the cells, are ascribed to limitations of the charge-transfer process across the solid/liquid interface. Thermally activated rates of ad- and desorption of sulfur containing solution species on the semiconductor surface and/or the presence of adsorption-induced electronic states in the bandgap are postulated as causes for this behavior. Notwithstanding these limitations the cells ar resistant to photocorrosion, after the initial decrease is arrested, in contrast to what is known for similar Cd-chalcogenide-based systems. We suggest that this stability, which persists under load and at high light intensities, is due to the strength and character of the bonds in CuIn-dichalcogenides, or to the presence of a top layer of indium oxide in which recombination will take place, or to both.

n-CuInSe2, n-CuInS2 and n-CuIn5S8 were used as photoanodes in electrochemical photovoltaic solar cells, using aqueous polysulfide electrolyte. CuIn5S8 was found to be less stable than CuInS2. Because of kinetic limitations of polysulfide-based systems, the CuInSe2/aqueous polyiodide cell was studied and optimized to yield stable, near 12% AM1 conversion efficiency. The strategy used to achieve this is described. (Photo)electrochemical methods were used to characterize the semiconductor materials and a photoelectrochemical test was developed to gauge the photovoltaic activity of p-CuInSe2 layers used in solid state cells. Solid-state chemical studies on the (Cu2X)2-(In2X3)(X=S,Se) system, and the use of photoelectrochemistry in them, are briefly described.

The performance of photoelectrochemical cells, containingn-CuInX2 (X=S, Se) semiconductor electrodes, has been studied as a function of solution composition and temperature. Significant differences with cells using CdSe or CdIn2Se4 electrodes are found, also in terms of output stability. These results, together with surface analyses, suggest the occurrence of binary chalcogenides on the electrode surfaces, which seems to influence the behaviour of these cells favourably È stato studiato il funzionamento delle celle fotoelettrochimiche contenenti elettrodi semiconduttorin-CuInX2 (X=S, Se), in funzione della composizione della soluzione e della temperatura. Sono state trovate differenze significative con celle che usano elettrodi di CdSe o CdIn2Se4, anche in termini di stabilità dell'uscita. Questi risultati, insieme ad analisi di superficie, suggeriscono la formazione di calcogenuri binari sulle superfici degli elettrodi, e ciò sembra influenzare favorevolmente il comportamento di queste celle. Исследуются характеристики фотоэлектрохимических элементов, имеюших полупроводниковые электроодыn-CuInX2 (X=S, Se), в зависимости от состава раствора и температуры. Обнаружены сушественные различия в элементах, имеюших электроды CdSe и CdIn2Se4. Полученные результаты, вместе с анализом поверхности, предполагают наличие бинарных халькогенидов на поверхностях электродов, которые, по-видимому, благоприятно влияют на поведение этих элементов.