Photoelectrochemical UV Detectors Based On SrTiO₃ Nanostructure

Ultraviolet(UV)light has pros and cons.Although it brings a lot of convenience to humanity's production and living activity,it is also harmful to human health.In recent years,due to the destruction of the environment,the ozone layer has become thinner and even holes,so the amount of UV radiation reaching the earth has been increased.Therefore,the detection of ultraviolet light is particularly urgent.Among the detectors that have been reported,the photoconductive UV detector has the advantages of long carrier lifetime and high switching ratio.However,it must be powered by an additional source,and also the performances suffer from environments.UV detectors based on Schottky junctions and p-n junctions usually have both high sensitivity and fast response,but the preparation process is quite cumbersome,which greatly limits their applications.In recent years,photoelectrochemical(PEC)type UV detectors have attracted much attention for their fast response,self-supply energy,low manufacturing cost,and eco-friendly.SrTiO₃ is a wide bandgap semiconductor with a bandgap of 3.2e V,high electron mobility,fast carrier diffusion rate,and better UV radiation stability.In terms of UV detection,SrTiO₃ has intrinsic visible-blind and only responds in the UV region.Due to its excellent light-capturing ability,SrTiO₃has excellent sensitivity to weak UV light,so it is an ideal material for preparing PEC type UV detectors with superior performance.To obtain a PEC UV detector with excellent detection ability,this thesis uses SrTiO₃ nanostructure materials as the photoanodes to fabricate the PEC type UV detectors.The main research results are as follows:(1)PEC type UV detectors based on SrTiO₃ nanoparticles film photoanodes.In this thesis,SrTiO₃ nanoparticles were synthesized under different conditions by the hydrothermal method,and then assembled PEC UV detector based on SrTiO₃nanoparticle film photoanodes on the FTO substrate by scraping method.The precursor concentration,hydrothermal temperature,and hydrothermal time will affect the morphology of SrTiO₃ nanoparticles.The results show that the UV detector present best performance under synthesized conditions of the molar ratio of Sr²⁺and Ti⁴⁺in the precursor solution of 3:1,the hydrothermal temperature of 120?and time of 10 min,the photocurrent density can reach 220.6?A cm^-2.Also,the thickness of the SrTiO₃ film between 30-40?m,the detector possesses the optimal photoelectric performance.The device exhibits a high switching ratio of 2575,a response time of 9 ms,and a fall time of 11 ms under 365 nm UV irradiation with 35 m W cm^-2.By introducing a block layer on the FTO substrate,the photocurrent density of the detector is increased by 1.88 times after the introduction of the block layer,which can reach 413?A cm^-2,and the response time and recovery time are also shortened to 6 ms and 8 ms,respectively.The reason is that block layer could avoid short circuits for direct contact between electrolyte and FTO.Moreover,due to excellent light-capturing ability,the UV detector based on SrTiO₃nanoparticles film presents high sensitivity to weak UV light(5?W cm^-2).In addition,the detector also exhibits visible-blind and excellent linear response.(2)PEC type UV detectors based on SrTiO₃ nanowires film photoanodes.In the SrTiO₃ nanoparticles film,electrons need to cross a large number of grain boundaries during the transmission process,which reduce collection efficiency of carriers,and affect the detection performance of the device.In order to solve these problems,the SrTiO₃ nanowires were synthesized under different conditions by electrospinning and then assembled PEC UV detector based on SrTiO₃ nanowires film photoanode on FTO substrate.The nanowires present a diameter of about 150 nm with a uniform sharp at applied voltage of 13 k V.Therefore,the PEC UV detector based on the SrTiO₃ nanowires film shows a superior detection performance.Under the 365 nm illumination of 35 m W cm^-2,the short-circuit current density of the detector could reach358.8?A cm^-2,which 1.63 times to that of the detector based on SrTiO₃ nanoparticles.More,the response and recovery time of the detector both shortened to 8 ms.In addition,the device presents a higher detective efficiency for weak UV light.The device also exhibits visible-blind,outstanding linear response,excellent repeatability,and stability under periodic UV irradiation.The one reason is that the SrTiO₃ nanowires could provide a direct electron transmission channel,which reduce the interface impedance during the transmission process,so that the photogenerated carriers can be more easily and quickly transferred to the FTO substrate.Another reason is that the SrTiO₃nanowires possess a large specific surface area to contact with the electrolyte.Therefore,the PEC UV detector based on the SrTiO₃ nanowire film shows a superior detection performance.