Extremely large crystal grains are obtained by bromine doping in electrodeposited Cu2O on indium tin oxide (ITO) substrate through an acetate bath. The grains are as large as 10,000 mu m(2) in area, or similar to 100 mu m in linear dimension, while the film is only 1-5 mu m thick. The enhanced grain size is explained by the effect of over-potential for the Cu2+/Cu+ redox couple on nucleation density of Cu2O on ITO substrate. The over-potential is a function of several deposition conditions including solution pH, deposition potential, deposition temperature, bromine precursor concentration, and copper precursor concentration. In addition, undoped Cu2O displays a high resistivity of 100 M Omega cm. Bromine doping in Cu2O significantly reduces the resistivity to as low as 42 Omega cm after vacuum annealing. Br-doped Cu2O shows n-type behavior. (C) 2012 Elsevier B.V. All rights reserved.