Low-resistivity ZnO:F:Al transparent thin films

Polycrystalline ZnO thin films doped with Al and F in nominal concentrations of 0.25 at% each element, have been obtained by the sol–gel technique. The films show a good adherence to the substrate, transmissions higher than 90% for wavelengths above 430 nm, and low resistivities: 8.6×10−3 Ω cm in darkness, and 5.6×10−3Ω cm under controlled illumination. These values are among the lowest obtained to date for doped ZnO. The mobility, 27 cm2/V s, is one of the highest reported for this kind of materials. When both dopants, Al and F, are present in small quantities, they contribute to the resistivity decrease of the ZnO films, while the high optical transmission is maintained. Due to their good optical and electrical properties, ZnO:F:Al films are promising candidates for their use as transparent electrodes in solar cells.