| As a kind of special semiconductor material, transparent conductive oxide (TCO) films have been widely used in various applications involving modern science and technology, such as solar cells, liquid crystal displays, touch panels, gas sensors and light-emitting diodes. Among the common TCO films, fluorine-doped tin oxide (FTO) film has many virtues such as high visible light transmittance, good conductivity, stable chemical properties, excellent acid/alkali resistance at room temperature, easily achieving laser etching, possibility of large-area fabrication and relatively low cost, enabling it to be widely developed and utilized as an alternative of tin-doped indium oxide (ITO) film. However, the photoelectric properties of FTO single-layer films prepared by traditional preparation processes can not meet the application requirements of booming photoelectric devices. Based on these, taking FTO films as objects, the optimizing preparation of metal-layer-composited bilayer/multilayer transparent conductive films was achieved. The effects of some methods, such as furnace annealing, furnace/laser dual annealing, magnetic-field-assisted laser annealing, laser-induced texturing and layer-by-layer furnace annealing, on surface morphology, structure and photoelectric properties of films were mainly investigated. Some significative results were obtained.1. Ag/FTO films were treated by furnace annealing. The effects of Ag layer thickness, annealing time and nitrogen flow rate on surface morphology, structure and photoelectric properties of the films were investigated. The optimum condition for evolution of Ag layer to Ag nanoparticles (AgNPs) and the effects of size as well as shape of AgNPs on the photoelectric properties of the films were discussed. The results showed that densely distributed 70-nm AgNPs with uniform size and spherical shape were formed on the surface of the Ag/FTO film with a 5-nm Ag layer thickness which was annealed at 450 ℃ for 20 min using a nitrogen flow rate of 10 sccm. The obtained AgNPs/FTO film had the best overall photoelectric property with a figure of merit of 1.39×10-2 Ω-1, which was higher than that of the original FTO film.2. Ag/FTO films were treated by furnace/laser dual annealing. The effects of laser fluence and scanning speed on surface morphology, structure and photoelectric properties of the films were studied, and the corresponding results were compared with those obtained by pure furnace and laser annealing. The results indicated that furnace annealing brought about the formation of small-sized AgNPs from the Ag layer, while subsequent laser annealing melted the AgNPs to conglomerate with SnO2 particles in the bottom layer, resulting in further improvement in photoelectric properties especially conductivity of the films. The results showed that the Ag/FTO film, which was obtained by furnace/laser dual annealing using a laser fluence of 0.9 J/cm2 and a scanning speed of 10 mm/s, exhibited the optimal overall photoelectric property with a figure of merit of 1.71×10-2 Ω-13. Ni/FTO films were treated by magnetic-field-assisted laser annealing. The effects of laser fluence as well as presence and direction of a magnetic field on surface morphology, structure and photoelectric properties of the films were researched. The results indicated that the optimum laser fluence for magnetic-field-assisted laser annealing was 0.9 J/cm2. The grain size of the film obtained by magnetic-field-assisted laser annealing was greater as compared to laser annealing, thereby yielding more remarkable enhancement in transmittance of the film. After employing vertical-magnetic-field-assisted laser annealing, the film surface was covered with a discontinuous Ni layer consisting of sparsely distributed and agglomerated particles, leading to a lower conductivity as compared with that of the film obtained by laser annealing. Transverse-magnetic-field-assisted laser annealing resulted in a continuous and dense Ni layer, thus enabling the corresponding film to possess the best overall photoelectric property with a figure of merit of 2.27×10-2 Ω-1.4. Various metal/FTO (M/FTO) films were treated by laser-induced texturing. The effects of laser fluence on formation of surface texture and photoelectric properties of the films were discussed. The selectivity of the metal layer material for laser-induced texturing and the feasibility for performance optimization of the films achieved by furnace-annealing-assisted laser texturing were comparatively studied. The results indicated that fabricating grating structures and laser annealing could be simultaneously achieved on the surfaces of Pt/FTO, Ag/FTO and Cu/FTO films by laser irradiation. The surface of the Al/FTO film only underwent laser annealing without forming grating structures during laser irradiation. The optimum condition for forming laser-induced grating structures on Pt/FTO film surface was a defocus amount of 2.5 mm and a laser fluence of 1.05 J/cm2, under which the maximum level of improvement in both transmittance and conductivity of the film was obtained. Furnace annealing coupled with laser-induced texturing could greatly enhance the conductivity of M/FTO films. The results showed that the pre-annealed Ag/FTO film treated by laser-induced texturing, whose figure of merit was 2.16×10-2 Ω-1, had the optimal overall photoelectric property.5. Various AZO/M/FTO films were treated by layer-by-layer furnace annealing. One-step furnace annealing was also carried out for comparison purpose. The effects of annealing temperature and AZO layer thickness on surface morphology, structure and photoelectric properties of the films were investigated. The results indicated that layer-by-layer annealing was conducive to enhancement in transmittance and conductivity of the films as compared to one-step annealing. The layer-by-layer annealed AZO/Pt/FTO film at 400 ℃ exhibited the highest figure of merit of 3.64×10-2 Ω-1. The layer-by-layer annealed AZO/AgNPs/FTO film with an AZO layer thickness of 500 nm, on which a more continuous AZO layer was formed, possessed the best overall photoelectric property with a figure of merit of 2.97 × 10-2 Ω-1. |
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