When operated at the current densities in excess of 10 mA/cm2 that are typical of efficient solar‐irradiated photovoltaic cells, normaln‐normalCdSe/1MNa2S‐1MS‐1MnormalNaOH/C semiconductor‐liquid junction cells deteriorate with time. In normalCdSe electrodes that have lost activity, formation of a normalCdS‐normalenriched film has been detected by means of Auger spectroscopy and electron beam‐induced luminescence. Such a layer is a barrier to the flow of holes to the surface. The rate of deterioration increases with light flux, usually decreases with stirring, and depends on the crystal face exposed to the solution. Addition of small amounts of elemental selenium to the solution substantially improves the stability by preventing excessive sulfide enrichment of the surface. For example, with 0.5M Se added, the output of <112̅0> face electrodes run at 35 mA/cm2 is essentially unchanged beyond 2×104C/cm2 charge passage.

The semiconductor liquid junction cell n-GaAs/0.8M K(2)Se-0.1M K(2)Se(2)-1M KOH/C has been shown to attain 9 percent photovoltaic power conversion efficiency in sunlight. Accelerated tests under 3100 degrees K light sources of several solar intensities indicate very low photocorrosion currents and high output stability.

Voltammetric and light to electrical energy conversion characteristics of metallized semiconductor Schottky junctions with redox solution contacts are reported. Electrodeposited noble metal films on normaln‐normalGaAs establish contacts to reversible aqueous redox couple solutions that can sustain solar photocurrent levels with low loss, requiring only a thin metal layer adequate to photovoltaic barrier formation. Possible advantages in lateral conductivity, relative to solid‐state Schottky devices, and in surface stability and redox electrolyte independence, relative to semiconductor‐liquid junction solar cells, are weighed against both the absorptive losses in the metal layer and the practicalities of obtaining sufficient integrity in the film to serve the semiconductor corrosion protection function. Gold, platinum, and rhodium plated normaln‐normalGaAs with carbon counter‐electrodes and ferro‐ferricyanide solutions give 2–6% conversion efficiency under solar irradiance.

Anodic dissolution and passivation characteristics of n- and p-type III-V compounds (III=Ga, In and V=P, As, Sb) have been compared in aqueous electrolytes. A range of interfacial behavior was observed on controlled potential cycling of these semiconductors in acidic, basic, and neutral solutions, the differences being more pronounced in acids. The dissolution of InP on anodization is severely inhibited even in acid medium by the formation of a coherent film removable only by extensive cathodic reduction. GaP, InSb, and GaSb passivate less readily, forming solubility-limited precipitates on the surface at high current densities. Passivation of InAs or GaAs at pH∼0 is virtually unreachable, except at extremes of current densities, with the films formed being quite porous and permitting considerable surface corrosion. The gradation of properties observed in the III–V compound series indicates that both group III and V members are involved in the film formation. Previous observations of the functions of films on InP and GaAs in photoelectrochemical cells, in acid and neutral media, respectively, are consistent with the above results. The formation of indium layers in InP, after reduction in acid media, has been demonstrated by ring–disk electrode techniques.

Pressure sintered electrodes of cadmium selenide subsequently doped with cadmium vapor have shown solar energy conversion efficiencies approaching 34 of those of single crystal specimens in sunlight experiments. The cell normalCdSe/1FNa2S‐1FS‐1FnormalNaOH/C has operated at 5.1% conversion efficiency under AM2 conditions with polycrystalline electrodes. The relatively small sacrifice of efficiency from single crystal values of 7.5±0.5% suggests the possibility of substantial cost advantage. The temperature and pressure conditions, cadmium doping procedure, material characterization, and the voltammetric behavior of the cell are discussed.