Research On Laser Surface Treatment And Photoelectric Performance Optimization Of Fluorine-doped Tin Oxide-based Thin Films

As a kind of transparent conductive oxide（TCO）thin films,fluorine-doped tin oxide（FTO）film has been widely used in various applications,such as solar cells,gas sensors,liquid crystal displays and so on,due to its stable chemical properties,high visible light transmittance and good electrical conductivity.However,the photoelectric properties of FTO films which are prepared by traditional processes cannot satisfy the requirements of booming optoelectronic devices.Therefore,researchers have focused on post-treatment of FTO films.By reviewing the relevant researches about laser surface treatment of films,this paper proposed two ways of laser surface treatment of FTO films based on polyethylene terephthalate（PET）film covering and metallic titanium layer compositing.The effects of laser parameters on surface morphology,crystal structure,optical and electrical properties of the films were mainly investigated,and some meaningful results were obtained.1.The FTO films covered with PET film were irradiated by a nanosecond pulsed laser with a wavelength of 532 nm,and the effects of laser fluence and scanning speed on photoelectric properties of the films were studied.A scanning electron microscope,an X-ray,an UV-Vis spectrophotometer and a four-point probe instrument were adopted to characterize the surface morphology,crystal structure,transmittance and conductivity of the films.Also the overall photoelectric properties of the films were evaluated by using a figure of merit（FTC）.The results indicated that covering PET films did not only an broaden the scope of laser processing parameters to prevent the FTO films from being damaged,it also enabled the FTO film surfaces to achieve the optimum annealing effect.In the present work,the film obtained by laser irradiation using a fluence of 1.2 J/cm2 and a scanning speed of 10.0 mm/s exhibited the best overall photoelectric property with an average transmittance in 400⁸00 nm waveband of 82.0%,a sheet resistance of 7.9 ?/sq and a figure of merit of 1.7×10^–2Ω^–1,which was improved by 54.5% compared to that of the original FTO film(1.1×10^–2Ω^–1).2.Ti layers were deposited on FTO films by direct current（DC）magnetron sputtering to prepare Ti/FTO composite films,and the effects of Ti layer thickness on photoelectric properties of the Ti/FTO films were studied.It was found that the Ti/FTO film with a Ti layer thickness of 10 nm had the highest figure of merit of 1.3×10^–2Ω^–1.Then this optimal Ti/FTO film was irradiated by a nanosecond pulsed laser with a wavelength of 532 nm.The effects of laser fluence and line-scan spacing on morphology,structure and photoelectric properties of the films were investigated.The results showed that laser irradiation using appropriate laser fluences and laser line-scan spacings could achieve annealing effect which could effectively promote grain growth and eliminate partial crystal defects as well as give rise to oxidation of Ti layer to TiO₂ layer,thus enhancing the overall photoelectric properties of the films.In the present work,when a laser fluence of 0.8 J/cm2 and laser line-scan spacing of 20.0 μm were adopted,the Ti layer was completely oxidized to TiO₂ layer and the optimum laser annealing effect was achieved.As a result,the as-obtained TiO₂/FTO film exhibited the best overall photoelectric property with an average transmittance in 400⁸00 nm waveband of 83.4%,a sheet resistance of 8.7 ?/sq and a figure of merit of 1.9×10^–2Ω^–1,which was improved by 58.3% compared to that of the original FTO film(1.2×10^–2Ω^–1).