| Due to the great application value in civil,commercial,military,aerospace and medical fields,ultraviolet detection technology has been widely researched.Recent years,compared with the ultraviolet photodetectors?UVPDs?based on p-n type and Schottky barrier,photoelectrochemical ultraviolet detector?PEC UV-PD?based on wide bandgap semiconductor has attracted great interest because of its unique advantages.PEC UV-PD mainly has two advantages.One is its high responsivity,and the other is that it is produced by physical chemical process,with nontoxic and abundant raw materials,simple process and low-cost.SnO2 is an important n-type semiconductor and is mainly in tetragonal rutile phase.It has good sensitivity in many fields such as chemical sensing,biosensing and UV sensing.Because the electron mobility(about 100-200 cm2·V-1·s-1)and the forbidden band width?3.6-3.8 eV?of SnO2 are higher than TiO2(about 0.1-1 cm2·V-1·s-1,3.2 eV),and the fast light response,visible blindness and stability of SnO2,SnO2 is promsing to replace TiO2 in PEC UV-PD field.Up to now,nanostructure like nanoparticles,nanowires/nanorods and nanotubes have been widely researched to design appropriate morphology.Nanoparticles with high specifical surface area can enhance the performance of UVPDs,but the interface between photoanode and electrolyte will make photogenerated electrons recombine with the ions in electrolyte easily.In comparison,one dimension nanostructure exhibits higher photo-generated charge transfer rate and lower probability of photo-generated charge recombining with the electrolyte.Firstly,SnO2 nanowires?NWs?array has been prepared on FTO substrate by simple hydrothermal method and was used as photoanode in PEC UVPDs.By optimizing the hydrothermal reaction conditions?the mass of SnCl4·5H2O is 0.408 g,the reaction temperature is 95°C,and the reaction time is 48 h?,the SnO2 nanowire array photoanode with the best photoelectric performance was obtained.Under ultraviolet light illumination(365 nm,40 mW·cm-2),the photocurrent?J?of the PEC UV-PD was 0.798 mA·cm-2,the optical responsivity?R??was 106 mA·W-1,and the switching ratio was 475.In order to further improve the photoelectric performance of PEC UVPD based on SnO2 NWs array,TiO2 was coated on SnO2 NWs array by simple chemical reaction,with a series of different coating times?20 min,30 min,40 min,50 min?to form different SnO2@TiO2 core-shell nanostructure,which can effectively prohibite the photogenerated charges recombination,and thus improving the photoelectric performance of PEC UVPD based on SnO2 NWs array.The PEC UV-PD of the SnO2@TiO2 core-shell nanostructure prepared under the optimal condition?40 min?exbihited J of 4.23 mA·cm-2 under ultraviolet light illumination(365 nm,40 mW·cm-2),and the light responsivity?R??reaches 106mA·W-1,which is 5 times higher than that of PEC UVPD based on the SnO2 NWs array(J was 0.798 mA·cm-2,R?was 20 mA·W-1).Furhtermore,the switching ratio is 5423,which is much higher than that of PEC UVPD based on the SnO2 NWs array.In addition,PEC UV-PD based on SnO2@TiO2 core-shell nanostructure has good stability,repeatability and fast light response.The rise time?r and fall time?d are 0.022 s and0.024 s,respectively.And when the light intensity ranged from 1 mW·cm-1 to 40mW·cm-1,the photocurrent density of the device increases linearly,indicating that the device has great potential for accurate measurement of ultraviolet light. |
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