PHOTOLUMINESCENCE AND RAMAN SPECTROSCOPY OF PHOTOELECTROCHEMICAL SOLAR CELLS (SEMICONDUCTOR, ELECTROLYTE)

The CdSe/polysulfide system was studied in order to produce low cost liquid junction solar cells. Three basic areas were investigated: (1) space charge layer effects, (2) aging of photoanodes due to slow chemical changes on electrode surfaces, and (3) the effect of photoetching and the impurity centers in phtoanodes. Relaxation spectrum analysis, photoluminescence, modulated photoluminescence, and Raman spectroscopy were utilized to study these areas.;The slow chemical changes on the CdSe/polysulfide liquid junction solar cells, as a function of aging procedures, were studied using photoluminescence and Raman spectroscopy. For the first time we report that cells do age under open-circuit conditions. The decrease in stability and the changes in photoluminescence with aging time, are similar to those observed for cells which are aged under short-circuit conditions. At the initial stages of the aging processes, changes in the defect concentration in the photoanode were observed. In addition to the CdSe photoluminescence there is a broad photoluminescence in the spectral range of 1.7 eV (CdSe) up to 2.4 eV (CdS) This photoluminescence is identified to be due to the mixed-phase compound of CdSe(,1-x)S(,x). At the final stages of the aging processes CdS Raman spectra were detected. Such photoluminescence or Raman spectra were not detected for the cells which were aged under total darkness. Variation of efficiency and photoluminescence peak intensity with aging time shows a high correlation between photoluminescence peak intensity and the efficiency of the cell.;The effect of photoetching on single crystal n-type CdSe was investigated, using photoluminescence spectroscopy. A blue-shift is observed in the photoluminescence spectrum of crystals when the doping density is decreased. A similar blue-shift is observed for crystals which were photoetched. It is attributed to the preferential etching of dopant atoms near semiconductor surface. This observation is supported by the dependence of the photoluminescence on the electrode potential. (Abstract shortened with permission of author.).;We have examined the potential distribution at the interface of n-type CdSe/polysulfide interface. At reverse bias and at electrode potential, the modulated photoluminescence is described by the "dead layer model." The electrical characterization of the interface, based on modulated photoluminescence, agrees with the relaxation spectrum analysis measurements.