Highly stable transparent and conducting gallium-doped zinc oxide thin films for photovoltaic applications

Transparent and highly conducting gallium zinc oxide (GZO) films were successfully deposited by RF sputtering at room temperature. A lowest resistivity of similar to 2.8 x 10-(4) Omega cm was achieved for a film thickness of 1100 nm (sheet resistance similar to 2.5 Omega/square), with a Hall mobility of 18 cm(2)/Vs and a carrier concentration of 1.3 X 10(21) cm(-3). The films are polycrystalline with a hexagonal structure having a strong crystallographic c-axis orientation. A linear dependence between the mobility and the crystallite size was obtained. The films are highly transparent (between 80% and 90% including the glass substrate) in the visible spectra with a refractive index of about 2, very similar to the value reported for the bulk material. These films were applied to single glass/TCO/pin hydrogenated amorphous silicon solar cells as front layer contact, leading to solar cells with efficiencies of about 9.52%. With the optimized deposition conditions, GZO films were also deposited on polymer (PEN) substrates and the obtained results are discussed. (C) 2008 Elsevier B.V. All rights reserved.