Ternary Chalcogenide-Based Photoelectrochemical Cells: II. The n-Cdln₂Se₄/Aqueous Polysulfide System

CdIn2Se4 is a cross-substitutional analogue of CdSe with an incomplete cation lattice. We have carried out an investigation of the n-CdIn2Se4/aqueous polysulfide photoelectrochemical cell. A selective photoelectrochemical etching of the semiconductor surface leads to a dramatic increase in the photocurrent of the cell (up to 15 mA cm-2 at small reverse bias) and greatly improved output stability. The spectral response of the cell reveals a considerable sub-bandgap photocurrent for the etched electrode. This is attributed to excitation via surface states located ⋃0.27 eV within the bandgap. After photoetching the electrode, most of the sub-bandgap response disappears and the response to supra-bandgap excitation increases by at least an order of magnitude that shows that these surface states serve also as recombination centers or traps for the photogenerated holes. We have analyzed the shape of the spectral response and observed two distinct transition modes: an indirect transition at 1.55 eV and a direct one at 1.72 eV, both of which are within the acceptable range for efficient solar energy, conversion. Preliminary results using thin film polycrystalline photoelectrodes of this semiconductor are presented. They show that this material tends to lend itself fairly well to preparation of such electrodes.