The development of photoelectrochemical solar cells based on semiconductor liquid junctions is discussed. Over the past 6 years, the efficiency of solar energy conversion has increased from < 1% to 12%, and the operational life of these cells has increased from hours to months. Understanding the chemistry of surfaces and grain boundaries has made it possible to manipulate the position of the surface and grain boundary states and thus reduce losses due to electron-hole recombination. Cells exhibiting approx. 12% efficiency of conversion are: (1) chemisorbed Ru/sup 3 +/ ions on n-GaAs photoanodes; (2) diffused Ru/sup 3 +/ and Pb/sup 2 +/ into grain boundaries of polycrystalline n-GaAs films on graphite; (3) p-InP/VCl/sub 3/-VCl/sub 2/-HCl/C cell; and (4) p-InP(Ru)/HCl-KCl/Pt cell. Photoassisted electrolysis of water for conversion of solar energy to hydrogen using the last mentioned photoelectrochemical cell represents the most efficient system for solar energy conversion. 61 references are cited. (BLM)tic stainless steel is required to prevent stress corrosion cracking byd stuffs contamination in the USSR takes place in the framework of variations observed in separate countries of northern hemisphere.

Conversion of Sunlight into Electrical Power and Photoassisted Electrolysis of Water in Photoelectrochemical Cells

Chemisorbed ruthenium ions on the surface of n‐GaAs decrease the surface recombination velocity of electrons and holes from 5×105 to 3.5×104 cm/sec. It is shown that the ions, in a one‐third monolayer thickness, are confined to the surface and do not form a new junction by diffusing into the GaAs. This use of Ru appears to be the first observation of the reduction of the surface recombination velocity for GaAs by the simple chemisorption of ions.

Reduction of GaAs surface recombination velocity by chemical treatment

Oxidation of the surface of p‐InP with alkaline peroxide and treatment with dilute potassium cyanide increase the efficiency of the p‐InP/V2+−V3+ ‐HCl/C cell to 11.5%. The open circuit voltage of the cell follows the redox potential of the solution over a 0.5 V range. The lack of voltage pinning is consistent with photoemission studies of Spicer et al., showing that adsorption of oxygen on p‐InP raises the surface fermi level from a position near the valence band maximum to noe near the conduction band minimum.

11.5% solar conversion efficiency in the photocathodically protected p‐InP/V3+‐V2+‐HCI/C semiconductor liquid junction cell

Unlike their solid-state counterparts, semiconductor-liquid junctions are versatile in that the incident solar energy can be stored in the form of chemical fuels. Another attractive application is the use of irradiated oxide semiconductor-coated surfaces for self-cleaning and antifogging. The theme of this history-tinged Guest Commentary centers on the question of what has been accomplished in the above "photoelectrochemical" schemes over the 35 year time frame from 1975 to 2010. Progress in this field was aided by the infusion of new concepts and contributions from the materials chemistry and physics communities. A related aspect of discussion is how the active semiconductor material has evolved both chemically and morphologically in these applications. It is shown that despite impressive research advances, only a handful of the above concepts (e.g., dye-sensitized solar photon conversion and self-cleaning and antifogging surfaces) have made the successful transition from the laboratory to the marketplace.

https://pubs.acs.org/doi/pdf/10.1021/jz200396h

Solar Energy Conversion and Environmental Remediation Using Inorganic Semiconductor-Liquid Interfaces: The Road Traveled and the Way Forward.

Stabilization of the light-harvesting semiconductor electrode is a key factor in the design of a photoelectrochemical (PEC) system for solar energy conversion. Approaches to circumvent the problem of PEC corrosion of these electrodes involve four major categories of materials: (a) the electrode materials themselves; (b) protective coatings; (c) catalysts; and (d) electrolytes. Wide band-gap semiconductors are candidates for electrode materials; however, their use hinges on devising effective means of sensitizing their photoresponse to wavelengths comprising the solar spectrum. These and related aspects in the design of PEC systems are reviewed in this article. Devices both of the regenerative type as well as photoelectrolysis approaches are considered.

W. D. Johnston

Papers

Effect of Ruthenium Ions on Grain Boundaries in Gallium Arsenide Thin Film Photovoltaic Devices