Characterization of p-Type CdTe Electrodes in Acetonitrile/Electrolyte Solutions. Nearly Ideal Behavior from Reductive Surface Pretreatments.

摘要

Single crystal p-CdTe (Eg equal 1.4 eV) electrodes have been characterized in CH3CN/electrolyte solutions. Deliberate modification of the p-CdTe surface by etching in strongly oxidizing (Cr2072-/HNO3) or reducing (S2042-/OH-) solutions alters the p-CdTe surface to give rise to large differences in the electrochemical response in the dark and under illumination. The oxidative pretreatment apparently yields a p-CdTe surface that is Fermi level pinned, whereas the reductive pretreatment yields nearly ideal response. The pretreated electrodes were characterized by XPS, impedance measurements, and cyclic voltammetry in the presence of a number of reversible, one-electron redox couples. XPS indicates the presence of a number of reversible, one-electron redox couples. XPS indicates the presence of a Te-rich surface overlayer, composed of Te0 and Te02, on CdTe etched in oxidizing media. Electrodes etched in reducing solutions yield XPS spectra nearly identical to those of an Ar ion-sputtered CdTe sample, in terms of stoichiometry (1:1) and chemical state (Cd2+ and Te2-) of cadmium and telluride.