Characterization of polycrystalline electrodeposited CdSe photoelectrodes using photoluminescence spectroscopy

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Abstract
We have utilized both photoluminescence (PL) and Raman spectroscopy to nondestructively study the surface of polycrystalline electrodeposited CdSe photoelectrodes as a function of surface preparation and aging procedures. The excitation energy dependence of the PL efficiency at 77 K, which depends on surface band bending, is consistent with increased concentration of shallow levels in electrodeposited CdSe compared with single crystal material. No PL was observed for unannealed CdSe films; for annealed, unaged films the spectra at 77 K were qualitatively similar to those of single crystals in that spectral features could be identified with the A exciton at 1.815 eV and with a donor-acceptor-pair band at 1.70 eV exhibiting phonon replicas. The PL and Raman spectra of light-aged electrodes exhibit features which we identify with the formation of a surface layer of CdS and the presence of mixed compounds CdSxSe1−x, which are formed by chemical exchange with the polysulfide electrolyte during light-induced aging. The PL spectra at 4.2 K for the unaged and dark-aged electrodes exhibit sharp lines in the vicinity of 1.81 eV which we identify as due to bound-exciton recombination, but which differ in energy from those exhibited by the light-aged film.