Research On Photoelectric Properties And Stability Of ZnO-based Thin Films On Flexible Substrates

Flexible zinc oxide?ZnO?thin films as a new type of transparent conductive oxide?TCO?thin films,have the virtues of light weight,compact size,folding,wide application range and so on,according with the developing direction of lightweight and portable in the current science and technology fields.They have gradually replaced films on hard substrates and are increasingly used in many fields such as wearable devices,flexible display screens and photovoltaic cells.However,their photoelectric properties and stability are often inferior to the traditional films on hard substrates due to the restriction of flexible substrates,so how to improve the overall photoelectric property and maintain the stability has become the main research orientation about flexible ZnO-based films.After the literature survey,it was found that there are many studies on the dielectric/metal/dielectric?D/M/D?sandwich structure of flexible ZnO-based multilayer films,but the material of the intermediate conductive metal layer are mostly precious metals with high price and scarce resource.It is rare to study the D/M/D structured films with low cost and wide range of common materials,and there are few reports on improving the stability of the overall photoelectric property of flexible ZnO-based multilayer films.In view of the above two problems,this paper takes the flexible ZnO-based multilayer film as the object and focuses on the influence of thickness ratio and the deposition sequence of Al and Cu layers on overall photoelectric property of flexible ZnO-based multilayer films.Furthermore,the BN film is introduced to study the influence of BN layer on property stability of flexible ZnO-based multilayer films,and some meaningful research results are obtained.1.ZnO layer and intermediate metal layers of Al and Cu were deposited on flexible PET substrate by magnetron sputtering for preparing flexible ZnO/Al/Cu/ZnO films.Al and Cu layers with different thickness ratios were selected,and then the influence of Al and Cu thickness ratio on the overall photoelectric property of the flexible ZnO-based multilayer films was studied.In addition,the deposition sequence of Al and Cu layers was further reversed under the condition of the optimal thickness ratio of Al and Cu layers,and the influence of deposition sequence of the intermediate metal layers on the overall photoelectric property of the flexible ZnO multilayer films was investigated.The surface morphology and phase composition of the flexible ZnO multilayer films were analyzed by scanning electron microscope?SEM?and energy disperse spectroscope?EDS?,respectively.The transmittance and the sheet resistance of the flexible ZnO multilayer films were measured by UV-Vis spectrophotometer and four-point probe instrument,respectively.Finally,a figure of merit(F_TC)was used to calculate the overall photoelectric property of the flexible ZnO multilayer films.The experimental results indicated that the thickness ratio of the intermediate metal layers had a major influence on the overall photoelectric property of the flexible ZnO/Al/Cu/ZnO films,but the deposition sequence has little influence on their photoelectric property.Specifically,when Al:Cu=6:2?i.e.,the thickness of Al layer was 6 nm and the thickness of Cu layer was 2 nm?,the overall photoelectric property of the flexible ZnO/Al/Cu/ZnO film reached the optimal level.In this case,the average transmittance in400-800 nm waveband was 84.73%,the sheet resistance was 108?/sq and the figure of merit was 1.77×10^-3?^-1.The photoelectric property of the flexible ZnO-based multilayer films barely changed when the deposition sequence was reversed under the optimal thickness ratio of Al and Cu layers.2.Based on the above experimental results,BN layer,as the upper layer,was introduced under the optimal thickness ratio and deposition sequence of Al and Cu layers,and then the flexible BN/Al/Cu/ZnO film was prepared by the same preparation method.The effect of BN layer thickness on the overall photoelectric property of the flexible ZnO-based multilayer film was mainly studied.Experimental results showed that the flexible BN/Al/Cu/ZnO film owned the optimal overall photoelectric property with the highest figure of merit of 8.15×10^-4?^-1 when the thickness of the BN layer was 100 nm.Then,flexible BN/Al/Cu/ZnO films and flexible Al/Cu/ZnO films were prepared based on the optimal thickness of the BN layer,and the influence of BN layer on the performance stability of the flexible ZnO-based multilayer film was studied by comparing the performance difference between the above two kinds of flexible films.The experimental results indicated that the BN layer could greatly improve the performance stability of the flexible ZnO-based multilayer film.Under different temperature environments,the excellent heat resistance of the BN layer could reduce the influence of high temperature on the performance stability of the flexible ZnO-based multilayer film.After being Baked for 18 h under 80?,the flexible BN/Al/Cu/ZnO film could still achieve a figure of merit of 9.61×10^-4?^-1,while the figure of merit of flexible Al/Cu/ZnO film decreased significantly and only was 1.69×10^-4?^-1.In the room temperature environment at different times,BN layer could act as a protective layer to isolate the intermediate conductive metal of the flexible ZnO-based multilayer films from atmospheric environment.Moreover,the excellent oxidation resistance of BN could ensure that the flexible ZnO-based multilayer films have no oxidation reaction in the long-term static process,thus not affecting the stability of the overall photoelectric property.After standing at room temperature for 24 h,the figure of merit of the flexible BN/Al/Cu/ZnO film was 1.26×10^-3?^-1,while the figure of merit of the flexible Al/Cu/ZnO film was 6.70×10^-4?^-1.