| Transparent conductive oxide films (TCOs) with a band gap, high optical transparent in visible range and low resistivity have been widely used in flat panel displays, solar cells, touch screen panels and optoelectronic devices. As a candidate material, indium tin oxide has been widely investigated, but indium is a scarce resource. Thus, other transparent conductive films with low cost and excellent performance have been attracting research attention.ZnO energy gap is 3.37eV at room temperature which is a wide band gap semiconductor. Nanostructure ZnO is excellent material in nanomaterials and semiconductors so which have been used widely in liquid crystal display, solar photovoltaic cells, protective coating, optical sensors, gas sensitive components, emission spectrum and light catalysis. As one of transparent conductive materials, ZnO has been widely studied since it is cheap, abundant, non-toxic and has excellent optical and electrical properties. In particular, Al-doped ZnO(ZAO) exhibited good optical property and thermal stability, and has widely attracted research interesting.Many methods were employed to prepare films including magnetron sputtering, pulsed laser deposition, hydrothermal method, chemical vapor deposition and sol-gol etc. The sol-gel approach combining with hydrothermal route is facile and does not require expensive equipments. The reported research results showed that the electrical properties of films prepared by sol-gel method are not better than those of prepared by other methods, and thus the preparation process should be improved. This paper is focused on the preparation of ZnO:Al films combinning sol-gel and hydrothermal methods. The experimental parameters including the sol concentration, Al doped amount, pretreatment temperature, annealing temperature and atmosphere have been investigated in detail. The phase, composition and microstructure of products were studied by XRD, SEM, and TEM. Hall Effect tester, UV-Vis absorption, PL spectra were used to measure the electrical and optical properties. The effect of ionic liquid adding into the sol on the film properties has also been investigated.(1) The Al-doped ZnO transparent conductive films were prepared by sol-gel method. The effects of the concentration of sol, Al doped amount, pretreatment temperature, annealing temperature and atmosphere to the photovoltaic performance of thin-films were studied. The results showed that the film crystallinity was improved with increasing the sol concentration. The film resistivity decreased at low Al concentration, and then increased with the increase of Al doped amount. When Al doped concentration is low, the carrier concentration increases with increasing the Al doped concentration. However, Al dopant will form defects in the crystalline lattice when the doped amount is high, and it will reduce the carrier mobility and make the resistivity increase. The studies on annealing temperature show that the high annealing temperature improve the film crystallinity and reduce the defects since the atoms will obtain more energy to move to the low-energy nuclear position on the surface of the films. The type of intrinsic defects and defect concentration could be changed by choosing the annealing atmosphere. When the sample was annealed at high temperature, oxygen adsorbed in the surface of films will enter the grain boundary, which will hinder the movement of electrons, while the adsorbed oxygen will reduced for the sample annealed under the reduction atmosphere NH3, and increased the concentration of oxygen vacancies in the films improving the carrier concentration and hall mobility and reduces the resistivity. The films showed the lowest resistivity of 4.401×10-4Ω·cm, carrier concentration of 2.895×1020 cm-3 and the Hall mobility of 48.99 cm2/V·s, and the visible light transmittance is 83%.(2) Hydrothermal method was employed to fabricate the ZAO thin films. The film structure and photoelectic properties have been investigated. The experimental results show that Al doped concentration has a great influence to the morphology of films. The films with different structure were prepared by varying the concentration of Al dopant. Hydrothermal reaction time is an important impact factor to the film crystallization. Results show that the amorphous thin-film has high visible light transmittance (95%).(3) The addition of ionic liquid in the sol system enhanced the photoelectric properties of ZAO films. The results show that ionic liquid can reduce the times of the coating and the (002) oriented growth was also changed. The films exhibited the minimum resistivity of 4.7×10-2Ω·cm, carrier concentration of 1.929×1018 cm-3 and the Hall mobility of 67.79 cm2/V·s. |
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