Thickness-Dependent Structural, Optical, and Electrical Characteristics of ZnO:Al Thin Films and Application in OLEDs

Optically transparent and electrically conducting aluminum-doped zinc oxide thin films of thickness 110, 350, and 500 nm have been deposited on unintentionally heated glass substrates by the radio frequency magnetron sputtering method to investigate their structural and optoelectrical properties. All thin films are shown to exhibit: 1) wurtzite-type hexagonal structure similar to ZnO with c-axis perpendicular to the substrate and 2) optical transmittance of >85% in the visible range. The increase in film thickness leads to growth of crystallites with an average size in the range of 16-26 nm, decrease in the sheet resistance, and increase in the figure of merit. Owing to high optical transmittance of 92%, low sheet resistivity of 26 Ω/□, and high figure of merit (9.23 × 10³ Ω^-1cm^-1), 500-nm-thick Al-doped ZnO films can be potential transparent conductors for photovoltaic applications. The organic light-emitting diodes fabricated with them and commercial indium-tin oxide thin films are shown to display comparable luminous flux power efficiency.