Photoelectrochemical Reactions and Formation of Inversion Layers at n‐Type MoS2‐, MoSe2‐, and WSe2‐Electrodes in Aprotic Solvents

Abstract

Capacity measurements and cyclic voltammetry have been used to conduct a systematic investigation of the potential distribution at the semiconductor‐organic electrolyte interface in the dark and under illumination with the n‐type synthetic layered compounds MoS₂, MoS₂, and WSe₂. From the obtained flat band potentials it could be concluded that the valence band edges vs. Ag/Ag⁺ are located in acetonitrile at ca. 1.0 V (MoS₂), 0.7 V (MoSe₂), and 0.4 V (WSe₂). As theoretically expected, the oxidized component of redox systems with Fermi levels near or below the valence band edge can inject holes thus inducing an inverted region and generating a p‐n junction in the solid. The cathodic current in the cyclic voltammograms of such redox systems occurs via hole injection with consecutive recombination of the injected holes while less oxidizing redox systems can only be reduced via the conduction band. — Since the semiconductors used in these experiments do not corrode in presence of a high surface concentration of holes, such a contact with an oxidizing redox electrolyte offers most favourable conditions for the application in a photoelectrochemical solar cell. The inversion layer has a maximal band bending and promises to obtain the highest possible photovoltage, which is however limited by the width of the band gap.