The Design And Interfacial Control Of ZnO Based Flexible And Wearable Ultraviolet Photodetector

With the development of the modern electronics,flexible and wearable electronic devices,such as electronic skin,flexible circuit devices,etc.,have played an increasingly important role in our daily life.Photodetector(PD),as one of the sensors,is an important part of information transmission,which has been widely used in military detection,biological sensing,and optical communication and so on.Therefore,it is significant to realize the flexible wearable application of photodetector.Since the fiber itself is light,flexible and easy to knit,wearable applications can be realized when they are woven into clothes.The construction of fiber-shaped photodetector is a way to realize flexible wearable applications.In addition,electronic skin,as a circuit element,can be directly attached to human skin,thus wearable applications of electronic devices can also be realized.However,there are still obvious problems in the reported fiber-shaped PDs,such as poor quality of materials prepared on the fiber substrate,poor interface quality of devices,and poor device performance.In this paper,the fiber-shaped PDs are constructed based on high-quality one-dimensional zinc oxide nanomaterials.Through interface engineering and strain engineering,interface quality and electronic transport characteristics are improved to enhance the performance of the fiber-shaped PDs.Through the weaving of fibrous active materials,the construction of high flexible fiber-shaped PD textile is realized.By means of solution technology,functional films are assembled on the ultra-flexible porous filter membrane substrate to realize the construction of electronic skin PD for flexible and wearable applications.The main research content of this paper includes the following aspects:1.A uniform and compact ZnO nanocrystalline film was deposited on the surface of zinc wire as a fibrous substrate by atomic layer deposition technology as seed layer.Then high quality ZnO nanorod arrays(NRAs)with high purity,high crystallinity,uniform orientation and uniform morphology were prepared by hydrothermal method.Based on ZnO NRAs,a fiber-shaped PD was constructed with the device structure of Zn/ZnO/PVK/PEDOT/Ag.Among them,PVK and ZnO form a coaxial PN junction,which generates a built-in electric field pointing from ZnO to PVK,which is beneficial to the separation and transport of photo-induced carriers.In addition,PEDOT:PSS layer tightly wraps PVK layer,and good interface contact is conducive to collecting and transmitting carriers.Under the condition of 325 nm illumination with bias voltage of-0.5 V and intensity of 0.5 m W/cm~2,the fiber detector can work stably with a Ilight/Idark ratio of 1.5,rising time of 6 s and falling time of 7 s.2.The wet transfer technology of large-area graphene film is realized.With the merits of high flexibility,high permeability and high conductivity of graphene,the monolayer graphene film was used as surface electrode,and the fiber-shaped PD with ZnO/PVK/graphene structure was constructed.The interface optimization of the fiber-shaped PD is realized,and the precise energy level matching in the device structure is guaranteed.The close contact between each functional layer,the PN junction formed by PVK/ZnO and the appropriate band structure can promote the separation and transport of photo-induced carriers,which is conducive to the improvement of device performance.The Ilight/Idark ratio of the device can reach 7.2,and the responsivity is 0.9A/W.The response speed is very fast,with the rising time of 0.28s,which is more than one order of magnitude higher than that of the reported fiber-shaped PDs.This interface optimization strategy can be widely used to obtain better device performance in fiber-shaped electronic devices.3.The fiber-shaped PD with Zn/ZnO/graphene structure was constructed.As a surface electrode,graphene was in close contact with ZnO,and the Schottky junction would generate built-in electric field pointing from ZnO to graphene,which would promote the separation and transport of photo-induced carriers and be beneficial to device performance.The Ilight/Idark ratio of the PD can reach 4,the responsivity is as high as 1.92 A/W,and the rising time and falling time are 0.52s and 3.3s respectively.According to piezoelectric electronics,when strain is applied to the device,under the piezoelectric field,the Schottky potential barrier and depletion area will become larger,thus enhancing the built-in electric field and further promoting the separation and transport of carriers.By using strain engineering,the performance of the fiber photodetector is further improved by applying compressive strain.When the compressive strain is 0.33%,the responsivity of the device reaches 2.16 A/W,with an increase of 12.5%.4.Based on nickel textile,high-quality ZnO NRAs were prepared by atomic layer deposition technology and hydrothermal method,realizing the weaving of fibrous ZnO.Graphene film was used as surface electrode to form parallel connection circuit and the photodetector textile(PDT)was constructed.Ag nanowires are introduced into the device structure to optimize energy level matching,so that the original bidirectional Schottky contact is transformed into a unidirectional Schottky contact of ZnO/Ni,forming a built-in electric field from ZnO to Ni,and promoting the separation and transportation of photo-generated carriers.In addition,the local surface plasman resonance(LSPR)peak of the Ag nanowire matches the absorption of ZnO,and the near-field enhancement effect will enhance the light absorption of ZnO,thus improving the device performance.The responsivity can reach 0.27 A/W and the Ilight/Idark ratio is as high as 10~2.The constructed PDT has excellent flexibility.After being bent for 1000 times,the photocurrent of the device can still maintain 94%of the maximum value,with good cycling stability.Excellent device performance and outstanding flexibility make the PDT has a great application prospect in the wearable field.5.ZnO nanowires with uniform size and good crystallinity were prepared by chemical vapor deposition method.By using polyvinylidene fluoride(PVDF)porous filter membrane as flexible substrate,Ag nanowire film and ZnO nanowire film were assembled by vacuum filtration method,and graphene film was transferred as surface electrode to construct a skin-like PD with Ag/ZnO/graphene Schottky structure.The functional layers assembled by vacuum filtration method are in close contact with each other.The highly flexible silver nanowire and graphene film are used as electrode materials to ensure the transport of device carriers.The Schottky contact between ZnO and graphene generates the built-in electric field pointing from ZnO to graphene,as well as the light response characteristics of the ZnO nanowire film itself,which enables the PD to obtain excellent device performance.The response of the device is up to 0.03 A/W,the Ilight/Idark ratio is as high as 10~2,and the rising time and falling time of the device are 4.68s and 4.18s.In addition,the skin-like PD has excellent flexibility.After 1000times of bending,the photocurrent can maintain 95%of the maximum value,with good cycling stability,and can be directly attached to human skin to achieve wearable applications.An array of PDs was constructed by solution technology,and the sensor imaging application was further realized.