Sensitized photoelectrolysis of water with sunlight. Progress report, June 1--August 31, 1977. [119 references]

The subject of photoelectrolysis of water at illuminated semiconductor electrodes to produce hydrogen is reviewed from 1839 up to the present. 119 literature references are cited. Critical interpretations of important concepts in this area of investigation are given. Techniques for improving the response of cells are discussed, and the expected maximum efficiency is calculated. Additionally, some preliminary experimental results with impurity sensitization of TiO/sub 2/ electrodes and heterostructure formation are presented

Sensitized photoelectrolysis of water with sunlight. Final report, June 1, 1977-December 31, 1978

A study was made of solar driven water photoelectrolysis cells employing semiconductor electrodes. An extensive review of the literature was undertaken, and the three major problem areas for these devices were identified: corrosion, poor sunlight absorption, and external bias requirement. Although many semiconductors had been tested, none had proven free of all three defects. Two approaches were thus followed for the experimental studies: impurity sensitization of wide band gap stable oxides, and heterostructure formation between unstable sunlight absorbers and corrosion resistant oxides. Water decomposition was achieved with visible light excitation of Cr-doped TiO/sub 2/. Transport properties were studies for TiO/sub 2/ and SrTiO/sub 3/ electrodes doped with V, Cr, Mn, Fe, Co, and Ni. The correlation between bias requirement and electron affinity of oxides was identified. Performance of heterostructure electrodes was shown to be limited either by pin hole problems or by potential barriers between the valence bands

Spray solar cell research: CdS/Cu/sub 2/S cells by ion exchange-CSD. Quarterly report No. 1, October 1-December 31, 1979

A study of the applicability of the Chemical Spray Deposition-Ion Exchange Technique to the formation of high efficiency, low cost Cu/sub 2/S/CdS solar cells has been undertaken. A Chemical Spray Deposition (CSD) apparatus and an Ion Exchange annealing station have been designed, and construction of these facilities is nearing completion. The object is to form films of CdO and Cu/sub 2/O by spraying appropriate solutions onto a heated substrate, and then to convert these oxides into CdS and Cu/sub 2/S through ion exchange by annealing in H/sub 2/S vapor. Such films will then be the basis for fabricating Cu/sub 2/S/CdS solar cells. Temporary spray and annealing equipment has been used while the permanent facilities are completed. CdO oxide films with thicknesses of 0.1 to 0.5 microns have been deposited. There is preferred crystal growth in the (111) direction on glass substrates. However, on SnO/sub 2/ coated glass, a (200) preferred orientation is obvious. The crystallite size is 5 to 10 microns, and porous spheres 10 to 20 microns in diameter are visible on the surface. After annealing in H/sub 2/S, the films are converted to CdS, but the reaction is not complete after 2 h. The optical transmission is now characteristic of CdS. The grain size was found to increase to the 100 micron range, but the surface spheres remain. A mixture of CuO and Cu/sub 2/O was formed in a preliminary spraying. The film converted to the digenite and djurleite phases of copper sulfide. Much improved control of the deposition process will result when the permanent facilities come on-line

Thin film polycrystalline silicon solar cells. Quarterly report No. 1, January 1, 1979-March 31, 1979

A theory capable of predicting the performance of polycrystalline silicon solar cells is formulated. It relates grain size to mobility, lifetime, diffusion length, reverse saturation current, open circuit photovoltage and fill factor. Only the diffusion lengths measured by the surface photovoltage technique for grains less than or equal to 5 ..mu..m do not agree with our theory. The reason for this discrepancy is presently being investigated. We conclude that grains greater than or equal to 100 ..mu..m are necessary to achieve efficiencies greater than or equal to 10 percent at AM1 irradiance. The calculations were performed for the case of no grain boundary passivation. At present we are investigating the improvements to be expected from grain boundary passivation. We have determined that the parameters that best fit the available data are as follows: (1) Number of surface states at grain boundaries acting as recombination centers - 1.6 x 10/sup 13//cm/sup 2/. (2) Capture cross section - 2 x 10/sup -16/ cm/sup 2/. (3) Surface recombination velocity at grain boundary - 3.2 x 10/sup 4/ cm/sec. The following types of solar cells are considered in the model: SnO/sub 2//Si Heterostructure, MIS, and p/n junction. In all types of solar cells considered, grain boundary recombination plays a dominant role, especially for small grains. Though the calculations were originally expected to yield only order of magnitude results, they have proven to be accurate for most parameters within 10 percent