Effects of laser irradiation on the photoelectric properties of thermal-annealed metal/fluorine-doped tin oxide transparent conductive films

Abstract

Three kinds of bilayer films, i.e. aluminum (Al)/fluorine-doped tin oxide (FTO), copper (Cu)/FTO and silver (Ag)/FTO, are prepared by coating a commercial FTO glass with sputtered metal layers, and subsequently thermally annealed. Then all the as-annealed bilayer films are irradiated using a 532 nm nanosecond pulsed laser. X-ray diffraction (XRD) analysis confirms that all the laser-irradiated films have underwent laser annealing, resulting in an improvement in their photoelectric properties. More significantly, after laser irradiation, the as-annealed Ag/FTO film exhibits the highest increment in average transmittance (400–800 nm) that is increased from 72.6% to 80.5%. This should be attributed mainly to the formation of laser-induced grating structures that have anti-reflection effect on their surfaces. It is also found that the laser irradiation decreases the sheet resistance of the as-annealed Ag/FTO film from 5.6 to 5.3 Ω/sq. The annealing caused by thermal effect of laser irradiation gives rise to an increase in grain size, thereafter reduces carrier scattering at grain boundaries and enhances carrier mobility, which should be responsible for the improvement in conductivity. The calculated results show that after laser irradiation the figure of merit of the as-annealed Ag/FTO film is greatly increased from 0.73×10-2 to 2.16×10-2Ω-1, indicating a significant enhancement in the overall photoelectric property of the film. Laser irradiation can simultaneously achieve fabrication of grating structures and laser annealing, providing a new idea for performance optimization of metal-layer-composited transparent conductive films.