Open-circuit, photoinduced aging of polycrystalline CdSe photoelectrodes in liquid-junction solar cells

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Abstract
We utilized photoluminescence (PL) spectroscopy under in situ conditions to study slow chemical changes on CdSe/polysulfide liquid-junction solar cells, as a function of aging procedures. The aging conditions were (1) focused light under open-circuit conditions; (2) focused light under short-circuit conditions; and (3) total darkness. For the first time we report that cells do age under open-circuit conditions, and that the decrease in stability and the changes in the PL, with aging time, are similar to those observed for cells which are aged under short-circuit conditions. At the initial stages of the light-induced aging processes, changes in the defect concentration in the photoanode were observed. In addition to the CdSe PL there is a broad PL in the spectral range of 1.7 eV (CdSe) up to 2.4 eV (CdS). This PL is identified to be due to the mixed phase compound of CdSe1−xSx. At the final stages of the aging processes characteristic CdS Raman spectra was detected. Such PL and Raman changes were not detected for the cells which were aged under total darkness. Under ex situ conditions the envelope of two PL spectra due to CdSe and CdSe1−xSx compound changes with the excitation light. Variation of efficiency and PL peak intensity with aging time shows a good correlation between PL peak intensity and the efficiency of the cell.

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