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