Development of Photoelectrochemical Cells Based on Compound Semiconductors and Nonaqueous Electrolytes. Annual Report, May 1-April 30, 1981

摘要

A high solubility, low light absorption redox couple was developed based on Cu exp + / exp +2 chlorides in CH sub 3 CN. The couple stabilizes n-GaAs against photoanodic dissolution at practical current densities, but not CdSe. Efficiencies for n-GaAs cells were 4 to 5%. p-Zn sub 3 P sub 2 was examined as a photocathode and found to be very unstable with respect to cathodic decomposition yielding PH sub 3 in protic media. PECs based on the I sub 3- /I exp - couple in CH sub 3 CN resulted in stable regenerative devices for polycrystalline n-GaAs, with 3 to 4% solar conversion efficiency. CdSe and CdTe were about 90% and < 10% stabilized by these electrolytes at photocurrent densities >1 mA/cm exp 2 . Thin films of CdSe on Ti, formed by a chemical bath deposition process, yielded >5% conversion efficiency in a polysulfide electrolyte under tungsten-halogen illumination. Thin films of CdSe on Ti formed by aqueous electrodeposition also yielded >5% efficiency, but the film homogeneity on performance was very sensitive to reagent concentration and current density. The techniques of laser spot scanning and photocurrent action spectra were modified for evaluation of chemical bath and electrodeposited CdSe photoanodes. Large area, sealed PECs based on both chemical bath and electrodeposited CdSe films have been designed, constructed and tested, and a qualitative assessment made of losses due to the various restructive geometries and counter electrode polarizations. A counter electrode based on Teflon bonded graphite and only 1% CoS sub 2 was developed that had excellent polarization characteristics for polysulfide electroreduction. The low concentration of Co may render PECs employing these electrodes less susceptible to photoanode poisoning than when pure CoS counter electrodes are used.