Flexible Transparent Conductive Electrodes For Self-powered Near-ultraviolet Photodetectors

Transparent electrode is indispensable components in various optoelectronic devices,including touch-screen mobile phones,organic light-emitting diodes（OLEDs）,displays,and transparent film heaters.Indium tin oxide（ITO）usually used to fabricate transparent electrode material due to its wide applicability.However,the scarcity and high cost of its raw material and the inflexibility property of ITO have prompted researchers to explore an alternative materials.More over,high cost and relatively slow production speed of ITO also hinder the development of low-cost optoelectronic products.The conductive network based on metal nanowires（Ag,Cu,Au,etc.）is an ideal alternative transparent electrode ITO due to its cost effectiveness,flexibility and potential for large-scale production.Therefore,as an alternative to ITO,the adoption of this nanowires in various technologies wiould lead to reduced costs.The electrical conductivity of Ag,Cu and Au at 20°C is 6.30×10⁷,5.80×10⁷ and 4.10×10⁷ S/m,respectively,which is higher than that of ITO.Among them,Ag nanowires（Ag NWs）have become the most anticipated substitute of ITO due to its highest metal conductivity from silver.On the other hand,Cu is only 8%less conductive than Ag(σ_Cu=5.80×10⁷ S/m,σ_Ag=6.30×10⁷ S/m),but is over 100 times cheaper compared to the costs of Ag,and greater abundant.These factors position Cu nanowires（Cu NWs）an attractive and cost-effective substitute of Ag nanowires.However,Cu is less stable than Ag,and easier to oxidize in the atmospheric condition,which lead to the rapid degradation of electrical properties during usage.Consequently,it becomes crucial to explore to find reliable methods to enhance the stability of Cu nanowires in ambient conditions.In this study,we developed Cu@BTA,M-Gr/Cu,M-Gr/Cu@Ag three different types of anti-oxidation nanowire transparent electrodes,and integrated them with polarized BaTiO₃ ceramics as detectors.The photoelectric response performance of the detectors using these three anti-oxidation transparent electrodes was compared with those using pure metal nanowire transparent electrodes.The research primarily focuses on these aspects,yielding the following key findings as follows:1.BaTiO₃（BTO）ceramics were initially prepared using the solid sintering method.Subsequently,Ag electrodes were plated on both sides,followed by polarization.and the upper sides were polished flat to 0.2 mm with sandpaper.Then Cu nanowires were synthesized via liquid phase synthesis,transparent electrodes were prepared through vacuum filtration and transferred onto the surface of BaTiO₃ to fabricate Cu NWs/BTO/Ag detectors.Similarly,Ag NWs/BTO/Ag detectors were prepared using the same method.To protect Cu nanowires from oxidation in atmosphere,the surface of Cu nanowires was coated with BTA to passivate the surface of Cu nanowires resulting in the formation of Cu@BTA nanowires（Cu@BTA NWs）electrode.The Cu@BTA NWs/BTO/Ag vertical structure UV photodetector was further prepared.The Cu NWs/BTO/Ag,Ag NWs/BTO/Ag,and Cu@BTA NWs/BTO/Ag detectors were subjected to photoelectric performance tests under various wavelengths of light to obtain the I-t curve.It was observed that the photocurrent output of Cu NWs/BTO/Ag and Ag NWs/BTO/Ag detectors decreased as the testing period increased.while the photocurrent output of Cu@BTA NWs/BTO/Ag detectors remained consistently stable.This stability can be attributed to the presence of a protective antioxidant layer formed by BTA molecules on the surface of the nanowires.The Cu@BTA nanowire-transparent electrode achieved a transmittance of 90.5%at a wavelength of 720 nm,with a corresponding square resistance of 90Ω/□.The detector has achieved the best photoelectric properties at a wavelength of 405nm.At this specific wavelength,the responsivity,detectivity and response speed（t_r/t_d）of the device are 6.45×10^-7A/W,1.97×10⁸ Jones and 28.8/37.2 ms,respectively.Notably,the Cu@BTA nanowire-transparent electrode has the property of oxidation resistance in atmospheric environment,and it can be produced cost-effectively and at a large scale while maintaining its excellent properties.2.Cu@BTA NWs/BTO/Ag detector can maintain stable photocurrent and photoresponse performance in the photoelectric performance test,but the transmittance of Cu@BTA nanowires transparent electrode in the ultraviolet range is decreased compared with that of Cu nanowires transparent electrode.To address this issue,In this part,we focused on prepare oxidation resistant Cu nanowire transparent electrode through different methods.In this part,we explored the application of 2-4 layers of graphene（M-Gr）as a protective coating on the surface of Cu nanowires.Due to the impenetrability of graphene to corrosive substances present in the air,Cu nanowires were successfully sheilded from oxidation caused by these corrosive agents.Firstly,a glass-based Cu nanwire-based transparent electrode and a Cu NWs/BTO/Ag detector were prepared following the procedures outlined in the initial phase.M-Gr were transferred onto the Cu nanwire-based transparent electrode leading to the formation of M-Gr/Cu NWs transparent electrode.Compared to Cu@BTA NWs,M-Gr/Cu NWs transparent electrode exhibited higher transmittance at ultraviolet wavelength,while also demonstrating significantly lower square resistance.The photoelectric performance of this photodetector was measured at a wavelength of 405 nm.At this specific wavelength,the responsivity,detectivity and response speed（t_r/t_d）of the detector were 2.35×10^-6 A/W,7.20×10⁸ Jones and 19.4/23.8 ms,respectively.More importantly,the photocurrent of this detector keep stable all the time.In order to maximize the overall photoelectric performance of transparent electrodes and detectors,core-shell structured Cu@Ag nanowires were prepared by covering the surface of Cu nanowires with a layer of Ag.Taking advantage of the superior conductivity of Ag compared to Cu,the performance of transparent electrodes can be enhanced while maintaining a cost-effective approach.synthesized using the liquid phase reduction method,then a Cu@Ag NWs/BTO/Ag photodetector was prepared using the previously mentioned procedure.M-Gr were transferred onto a transparent electrode composed of Cu@Ag nanowires to fabricate M-Gr/Cu@Ag NWs/BTO/Ag detector.The photoelectric response propertiesof the two detectors was measured under 405 nm wavelength light.The photocurrent of Cu@Ag NWs/BTO/Ag detector gradually decreased as the the measure period increased.In contrast,the photocurrent of the M-Gr/Cu@Ag NWs/BTO/Ag detector maintained stable.At this particular wavelength,the responsivity,detection rate and response speed（t_r/t_d）of M-Gr/Cu@Ag NWs/BTO/Ag photodetector were 2.99×10^-6 A/W,9.16×10⁸ Jones and 12.06/27.01 ms,respectively.The incorporation of M-Gr/Cu@Ag NWs/BTO/Ag further enhanced the photoelectric response performance.The two works in this part provide a novel approach for for preparing stable transparent electrodes based on Cu nanowires in atmospheric environments,while also proposing a feasible method for improving the performance of Cu nanowire-based transparent electrodes.