Low-Cost CdZnTe Devices for Cascade Cell Application, Final Subcontract Report, 15 May 1989 - 15 May 1990

This report describes a research program to develop a low-cost technique for producing Cd{sub 1-x}Zn{sub x}Te devices for cascade solar cell applications. The technique involves a two-stage process for fabricating such devices with a band gap of about 1.7 eV and a transparent contact layer of low-resistivity ZnTe. In the first stage, thin films of Cd, Zn, and Te are deposited in stacked layers as Cd{sub 1-x}An{sub x}Te. The second stage involves hearing and reacting the layers to form the compound. At first, electrodeposition was used for depositing the layers to successfully fabricate Dc{sub 1-x}Zn{sub x}Te thin-film devices. These films were also intrinsically doped with copper. For the first time, transparent ZnTe films of low resistivity were obtained in a two-stage process; preliminary solar cells using films with low Zn content were demonstrated. A second phase of the project involved growing films with higher Zn content (>15%). Such films were grown on CdS-coated substrates for fabricating devices. The effects of the solar-cell processing steps on the Cd{sub 1-x}Zn{sub x}Te and CdS/Cd{sub 1-x}Zn{sub x}Te interfaces were studied; results showed that the nature of the interface depended on the stoichiometry of the Cd{sub 1-x}Zn{sub x}Te thin film. A sharp interface was observedmore » for the CdS/CdTe structures, but the interface became highly diffused as the Zn content in the absorber layer increased above 15%. The interaction between the CdS window layer and the Cd{sub 1-x}Zn{sub x}Te absorber layer was found to result from an exchange reaction between Zn in the absorber layer and the thin CdS film. 14 refs., 10 figs.« less