Preparation And Performance Study Of Cellulose-based ZnO UV Photodetectors

In recent years,flexible ultraviolet photodetectors(UV PDs)have been widely used in optoelectronic detection,military manufacturing,fire monitoring,and biological and chemical analysis due to their unique flexibility and wearability.The substrate of traditional flexible UV PD is petroleum-based polymer material,which is non-renewable and non-biodegradable and prone to environmental pollution.Cellulose is a kind of natural polymer material,which exists widely in nature and has the characteristics of renewable,biodegradable,non-toxic and low cost.It has been gradually applied to various detectors in recent years.However,cellulose itself more hydroxyl structural properties makes it hydrophilic,the presence of moisture will directly influence the performance of electronic devices,thus leading to some challenges in the preparation and storage of cellulose-based UV PD.Therefore,it is urgent to find a highly stable and weather-resistant cellulose-based flexible substrate and build a flexible UV PD based on it to promote the development of new flexible electronic devices.In this paper,two different physical deposition methods,radio frequency(RF)magnetron sputtering and electron beam(e-beam)evaporation,are used to investigate the optimal process conditions for polytetrafluoroethylene(PTFE)film growth on the both sides of cellulose paper to obtain hydrophobic cellulose paper with wet stability and flat surface.The UV PD with high detectivity,high stability and flexibility was prepared by introducing the semiconductor material zinc oxide(ZnO)into the cellulose paper by physical vapor deposition and mechanical mixing.The main research contents are as follows:(1)PTFE was grown on the both sides of cellulose paper by RF magnetron sputtering and e-beam evaporation to obtain hydrophobic PTFE/cellulose/PTFE composite paper.The effects of two different deposition methods on the properties of PTFE/cellulose/PTFE composite paper were investigated.The composite paper with surface roughness of88 nm and water contact angle(WCA)of 135°can be prepared by evaporating PTFE film on cellulose paper with e-beam current of 6 m A for 12 min.The composite paper with surface roughness of 125 nm and WCA of 124°can be prepared by sputtering PTFE film on cellulose paper for 4 h at 60 W power.In addition,the surface morphology,surface composition and humidity expansion coefficient of PTFE/cellulose/PTFE composite paper obtained by two different deposition methods were compared.The results show that PTFE/cellulose/PTFE composite paper prepared by e-beam evaporation has more advantages in hydrophobic properties,surface flatness,preparation time and cost.(2)A semiconductor material ZnO film with UV absorption function was grown on the surface of PTFE/cellulose/PTFE trilayer films by RF magnetron sputtering,and then Ag cross finger electrodes were prepared based on ZnO/PTFE/cellulose/PTFE multilayer films to construct UV PD with metal-semiconductor-metal(MSM)structure.The experimental results show that the on/off ratio of UV PD prepared based on ZnO/PTFE/cellulose/PTFE multilayer films can reach 1×10~4,which is 50times of the original cellulose paper-based UV PD;the response time(rise time)of UV PD prepared based on PTFE/cellulose/PTFE multilayer films is 0.56 s,which is only 3%of the original cellulose paper-based UV PD;the UV PD based on PTFE/cellulose/PTFE multilayer films has better moisture stability performance when exposed to air.(3)ZnO nanoparticles of different masses(0.1 g,0.2 g,0.3 g and 0.4g)were added into the cellulose solution by mechanical blending method and mixed thoroughly,and subsequently regenerated to obtain ZnO/cellulose composite paper;then based on the ZnO/cellulose composite paper,Ag cross finger electrodes were prepared by e-beam evaporation to construct flexible UV PD with MSM structure.The experimental results showed that the ZnO nanoparticle addition has a great influence on the performance of UV PD.When the content of ZnO is 0.2 g,the flexible UV PD has good stability and repeatability,and the response degree to UV light can reach 37%of that in the dark current steady state.In addition,the flexible UV PD has good thermal stability and flexibility,and can maintain a high optical response at an operating temperature of 60°C.After 100 bends,the photocurrent still has more than 92%of the initial value.