Characterization of the Interface Energetics for N-Type Cadmium Selenide/Non-Aqueous Electrolyte Junctions.

摘要

Single-crystal, n-type CdSe photoanodes have been studied in 0.1 M (n-Bu4N)aCl04/CH3CN solutions containing low concentrations of fast, outer-sphere, one electron redox reagents. A number of redox couples were studied spanning a wide range of redox potentials. We find that reversible electrochemical response is seen at both dark and illuminated (632.8 nm light) n-CdSe for couples with redox potentials more negative than -1.2 V vs. SCE, e.g. Ru(bpy)3(2+/+/0/-. For couples with redox potentials positive of -1.2 V vs SCE we find that CdSe is blocking to the oxidation of the reduced form of the redox couple in the dark, but illumination results in its oxidation. The photoanodic current peak in a cyclic voltammogram occurs more negative than at a Pt electrode, the difference between theses values is the photovoltage, EV, taken to approximate the barrier height, EB. The effect of a number of different etches on the interface energetics of CdSe was investigated, since it was previously determined that an oxidizing or reducing etch would yield quite different results for n-CdTe. For CdSe, however, the different etches do not give significantly different results with respect to EB vs redox potentials, despite large variation in surface composition deduced from Auger and XPS spectra.