Effect of Bath pH on Electronic and Morphological Properties of Electrodeposited Cu2O Thin Films

Abstract

The ability to systematically vary the flatband potential and the band edge positions of Cu2O by varying the deposition bath pH is considered important in the context of using Cu2O for photocatalytic water splitting. Capacitance-voltage (C-V) and dark and light current-voltage measurements were taken in order to investigate the electronic properties of electrodeposited Cu2O thin films grown in an acetate bath containing a 0.01 M Cupric Acetate having different bath pH values. The Mott-Schottky plots resulting from C-V measurements revealed that the flatband potential and doping density of the films strongly depended on the deposition bath pH. For pH values lower than 7.2, conductivity of Cu2O films remained n-type while it changed to p-type for higher pH values indicating that change of n-type to p-type character of the Cu2O films can be controlled by the bath pH. With increasing pH value, the grain size decreased, while crystal shapes transformed from truncated octahedral to cubic within the tested pH range. A well ordered cubic structure was observed in films deposited at pH 7.8. The rate of deposition decreased at higher pH values leading to thinner films indicating the effect of pH on the film thickness. Calculated band edge positions of conduction and valance bands of the Cu2O films were −4.19 eV and −6.29 eV respectively with respect to the vacuum level.