Electrodeposition of Phase–Pure n–Type Cu2O: Role of Electrode Reactions and Local pH

Abstract

Cuprous oxide (Cu2O) thin films, antithetically exhibiting n-type conductivity, were electro–deposited on Fluorine-doped Tin Oxide (FTO) coated glass substrates. Linear sweep voltammetry, chronoamperometry, and chronopotentiometry studies coupled with structural characterization of the deposit identify the occurrence of multiple reduction reactions, including “corrosion” of Cu2O to Cu. Interestingly, an underpotential conversion (negative of +0.039 V vs Ag/AgCl) of the Cu2O film to Cu islands is observed during potentiostatic deposition. The same process is also shown as a potential spike in chronopotentiometry curves, during galvanostatic deposition, at current densities that are cathodic of −0.2 mAcm−1. The reason for the formation of Cu is attributed to the decrease in local pH in the vicinity of the working electrode, whence thermodynamic conditions favor the formation of Cu. The proroguation of Cu formation is achieved by continuously stirring the solution, thereby stabilizing the pH at the electrode. Deferment of film corrosion to increasingly longer times is observed with increasing stirring rates. Mott-Schottky analysis of phase-pure films reveals the formation of degenerately doped n-type Cu2O films (n ∼1020 cm−3). The phase pure Cu2O films could be used as an electron transport layer in several photo-conversion devices and ultimately pave the way for an oxide homojunction device.