Comparison of Behavior of Single‐Crystal and Polycrystalline CdS in Photoelectrochemical Cells

Abstract

Capacitance in the dark and photoresponse were determined from single‐crystal <001> and polycrystalline (deposited cathodically from dimethylsulfoxide). Three different solvents employed (water, triethyleneglycol dimethyl ether and acetonitrile) gave results that lead to essentially the same conclusion. Thus, single‐crystal having a “clean” surface gives identical onset and shut‐off potentials that are the same as the flatband potential determined from Mott‐Schottky (MS) plots of capacitance data. These MS data are independent of the scan direction for the potential. Surface sulfur that results from photoxidation causes the onset to shift negative of the shutoff. Also, the MS intercept becomes dependent upon the scan direction of the potential. These results can be explained by the effect of the oxidation level of the surface sulfur on the flatband potential. In contrast, for fresh polycrystalline that has not been subjected to photo‐oxidation, the onset potential is negative of the shut‐off potential. These and other results can be used as evidence that the growing process incorporates one or more sulfur containing impurities that are uniformly distributed throughout the film.