| Transparent conductive oxide (TCO) films have multiple properties including an excellent optical transparency and a good electrical conductivity, which enable TCO films to have been widely used in various applications, such as photovoltaic modules, flat panel displays, touch panels, light-emitting diodes (LEDs) and gas sensors. It must be noted that the optical transparency and the electrical conductivity of TCO films are contradictory and restrain each other. However, as for applications of them in photoelectric devices especially in solar cells, a good photoelectric performance is absolutely required. In order to meet the application requirements of high transparency and low sheet resistance, many researches about TCO films have been focused on preparation methods of them, even the post-treatment processes (such as micro/nano structure combination on surface, thermal annealing and laser annealing) and double-layer/multilayer composite optimization.Among the TCO films, the fluorine-doped tin oxide (FTO) film has virtues of relatively low cost (containing no expensive indium element), good thermal stability and high chemical stability, so it has been studied and applied abroad in recent years. But compared with tin-doped indium oxide (ITO) film, FTO film has disadvantages of slightly low conductivity, insufficient research in related processes (including post-treatment processes) and expanded methods for performance optimization, which are all need to be further identified and studied by researchers in the filed of materials science. Based on these, some studies about FTO films, such as metal particles combination, thermal annealing, laser treatment, double-layer composite optimization and post treatment, are carried out. Also some significative results are obtained.1. Silver (Ag) particles are prepared on FTO film substrates by direct current magnetron sputtering and thermal annealing treatment. The conductions for formation of Ag particles on different substrates are comparatively studied. The effects of annealing temperature, annealing time and thickness of initial Ag film on formation and morphology of Ag particles, as well as photoelectric properties of FTO films, are mainly discussed. The results indicate that lower annealing temperature and shorter annealing time are needed to form Ag particles on a FTO film substrate compared with a silicon substrate or a glass substrate. Some good-shaped Ag particles are formed on FTO film substrates when Ag films are annealed at500℃for20-30min with an initial Ag-film thickness of200nm in this experiment. The transmission spectra of the films show resonance peaks of Ag particles surface plasmon.2. Some FTO films are thermal annealed in tubular furnace. The effects of annealing atmosphere, annealing temperature and time on structure, surface morphology and photoelectric properties of the FTO films are studied, and the mechanisms of these effects are deeply analyzed. Also the integrated photoelectric properties of all the FTO films are appraised by calculating figure of merit. The results indicate that the crystallinity of the FTO films are improved when annealed in nitrogen, air or oxygen, and the integrated photoelectric properties of the FTO films annealed in nitrogen are best. When annealing in nitrogen, the effects of annealing time on transmittance and sheet resistance of the FTO films are not as dramatical as those of annealing temperature, and the best integrated photoelectric property with a figure of merit of5.56×10-3Ω-1is achieved by annealing at500℃for20min.3. The surfaces of FTO films are irradiated by a nanosecond pulsed laser with a wavelength of532nm. The effects of laser fluence and scan speed on morphologies and photoelectric properties of the films were discussed. The results indicate that the film irradiated by laser with moderate laser fluence and scan speed achieved better laser annealing effects. The crystalline grains in laser irradiate zone grow up through a recrystallization process, which results in improvement of transmittance and decrease of sheet resistance. The laser fluence of1.02J/cm2and the scan speed of10mm/s are the optimal laser parameters in this experiment, with the average optical transmittance of the film in the waveband of380-780nm increased from75.4%to82.7%and the sheet resistance of the film decreased from10.20Ω/□to8.83Ω/□.4. By depositing aluminum-doped zinc oxide (AZO) films on FTO films using direct current magnetron sputtering, some AZO/FTO composite films are prepared. The effects of AZO-layer thickness on structure, micro-morphology and photoelectric property of the AZO/FTO films are investigated, and the mechanisms of these effects are preliminary discussed. The results show that the surface roughnesses of AZO/FTO films gradually reduce when the AZO-layer thickness increases, with the sheet resistances of the films decrease firstly and then change gently, as well as the transmittances of them increase firstly and then decrease. It is found in this experiment that the AZO/FTO film with an AZO-layer thickness of495nm has the best photoelectric property with a figure of merit of1.43x10-2Ω-1.5. The optimally prepared AZO/FTO films are post-treated by both thermal annealing and laser irradiation to further improve their properties. The variations in surface morphologies and photoelectric properties of the films treated with different parameters are studies. The results show that the compactnesses and planenesses of the films treated by thermal annealing are enhanced, and the transmittances of them keep on slightly improving with increases in annealing temperature or annealing time. While the sheet resistances of them decrease greatly before the annealing temperature is up to300℃, and then are almost not affected with the increases in annealing temperature or annealing time at500℃. Laser irradiation can also achieve a certain annealing effects on AZO/FTO films, and the optimal effect is obtained by treating them with a laser fluence of1.02J/cm2and a scan speed of10mm/s. |
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