Preparation And Photoelectric Properties Of Ultrathin Aufilms

With the rapid development of flexible photoelectric devices,it is urgent to develop flexible transparent electrodes with high flexibility,high stability and low cost.Traditional transparent conductive materials（ITO）can not meet the needs of related industries due to high price and low mechanical flexibility.Ultrathin metal films have excellent photoelectric properties and high mechanical flexibility,which become a potential substitute.This paper focuses on the preparation and application of ultrathin Au transparent films.The properties of metal film are subject to the thickness and morphology.Au film usually presents a three-dimensional island growth mode on the substrate and there is a critical thickness（10-15 nm）.The film shows discontinuous island surface and poor electrical properties when the thickness of the film is less than the critical thickness.As the thickness increases,the metal islands are connected to each other to form a continuous film accompanied with significantly enhanced light absorption,reflection and scattering.Therefore,in order to obtain an ideal transparent conductive metal film,it is necessary to reduce the critical thickness of the metal film.In this paper,the critical thickness of Au films is reduced by means of van der Waals epitaxial technique combined with oxide wetting layer and the ultrathin metal films with excellent properties are obtained.Oxide/metal/oxide（O/M/O）sandwich structure was used to further improve the transmission and stability of Au thin films.Pulsed laser deposition（PLD）method was used to fabricate Au,Au/AZO and（TiO₂）/Au/AZO（TiO₂）transparent and conductive films on Mica.The growth modes of the films were characterized by XRD,AFM,SEM,RHEED and TEM.The effects of Au,AZO and TiO₂ film thickness on the photoelectric properties of the films were determined.Au/AZO film and AZO/Au/AZO film were applied to OLEDs device and flexible transparent film heater respectively.The performance of the devices were characterized and its application prospect were explored.The main results could be summarized as below:（1）vdW epitaxy of AZO films has been prepared on Mica.By utilizing this vdW epitaxy layer,we used the AZO film as a seed layer availably induced the formation of the epitaxial ultrathin and ultrasmooth Au film.（2）The square resistance of Au/AZO/Mica thin films decreases with the increase of Au and AZO thin films thickness.The critical thickness of pure Au thin films is reduced and the optoelectronic properties of pure Au thin films is improved by AZO film.The Au（8 nm）/AZO（25 nm）film shows an excellent surface morphology with a root-mean-square（RMS）roughness of 0.8 nm,low optical loss（average visible transmittance of 80.1%）and outstanding conductivity（RS=8Ω/sq）.The Au（8 nm）/AZO（25 nm）film remains its low electric resistivity even after 1000times continuous bending cycles.Moreover,the Au/AZO anode-based OLED was fabricated with the maximum luminance intensity of 32540 cd/cm²,which demonstrate it is promising to apply in next generation flexible optoelectronic devices.（3）We report a high-quality AZO/Au/AZO sandwich film with excellent optoelectronic performance,e.g.,an average transmittance of about 88.1%over the visible range,a sheet resistance of 5Ω/sq,and a figure-of-merit（FoM）factor of 55.1（The thickness of the total coat layer and Au are 126 nm and 10 nm respectively）.Moreover,the response time of the film heater based on the AZO/Au/AZO trilayer films is about 5 s and the heater temperature can reach as high as150°C at an operating power of about 5.6 W.Infrared camera thermal images show that the temperature of the films is uniform,even under the condition of bending with a diameter of 2cm.These results indicate that the high-quality film is a promising candidate for the flexible film heater.（4）Overall,AZO/Au/TiO₂ has higher transmittance than TiO₂/Au/AZO thin films,and AZO（80 nm）/Au/TiO₂（20 nm）thin film has the highest average light transmittance in visible light（87.41%）.（5）The Au/AZO/Mica and AZO（TiO₂）/Au/AZO（TiO₂）/Mica prepared in this paper have excellent photoelectric properties and are expected to be used as flexible electrodes in organic solar cells and other optoelectronic devices,promoting the development of the field of flexible optoelectronic devices.