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 the “corrosion” of Cu2O to Cu. Interestingly, under–potential 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 evinced as a potential spike in the chronopotentiometry curves, during galvanostatic deposition, at current densities that are cathodic of −0.2 mA cm−2. The reason for Cu formation is attributed to the decrease in local pH in the vicinity of the working electrode, whence thermodynamic conditions favor the formation of Cu. Proroguing the Cu formation is achieved by continuous stirring of the solution; deferment to increasingly longer times is observed with increasing stirring rates. Mott-Schottky analysis of the phase pure films reveals the formation of degenerately doped (n ∼ 1020 cm−3) n-type Cu2O.