| Photo-electro-chemical(PEC)photodetector,with a lot of advantages such as low cost,fast response,linear response,etc.,is one of the photodetecting devices that is promising and widely applied in various fields.And quantum dots(QDs)sensitization can greatly improve performance of PEC devices,which have been broadly used in solar cells and photocatalysis application but little in PEC photodetectors.In this research,Cd S QDs as well as Cd S/Cd Se core-shell structure QDs were in-situ synthesized on Ti O2 mesoscopic beads photoanode.Then PEC photodetectors with these QDs sensitized photoanodes were fabricated and measured under certain light condition,some of which showed excellent performance.The influence of synthesis process on performance of the QDs sensitized devices was also studied.In this paper,two in-situ synthesis method using for prepare Cd S QDs,SILAR and CBD,were compared.The result indicated that the former one is more applicable to Cd S QDs synthesis.Under the condition of 5 cycles and 20 s per cycle,the device reached the best performance with short-circuit current density(Jsc)reaching 4.279 m A cm-2,on/off ratio of 3457 and rise/decay time of 0.059 s/0.043 s respectively,under the light condition of 20 m W cm-2 at 365 nm.The device responded fast and steadily to light signal with repeatedly on and off,and exhibited excellent linear response characteristic,representing an ability to detect optical signal quantitatively.UV-Vis and EIS analysis demonstrated that the response range of the devices with QDs was widened from near ultraviolet area to near ultraviolet and blue-violet area.Their absorbance was increased as the cycle time increased and reached maximum as the cycle time was 5.Further increase of cycle time did not increase absorbance but decrease the recombination impedance Rct2,which made Jsc become lower.Besides,the annealing process for Cd S QDs could improve their crystalline degree and absorbance,and in the meanwhile reduce the number of defects in QDs,thereby increasing Rct2 and Jsc.Next,the Cd S QDs synthesized above were modified by synthesizing Cd Se shell on them through an improved SILAR method,forming a core-shell structure.The device sample Cd S5/Cd Se1,with best performance,showed a Jsc of 5.471 m A cm-2 under the same light condition as above,which meant an improvement of near 30% compared with the one sensitized by Cd S QDs only.It also possessed fast and stable response to the variation of light signal of on and off.EIS analysis revealed that Rct2 and electron lifetime ?n reached maximum in the condition of Cd S5/Cd Se1 and became smaller as the SILAR cycle time increased.It is inferred that Cd Se shell worked as a barrier for electron,hindering the recombination between photogenerated electron in Cd S core and electrolyte outside Cd Se shell and increasing Rct2.When Cd Se shell became thicker,a large amount of defect in the shell with relatively low crystalline degree would greaten the probability of recombination around the interface,and further lower performance of the devices.Therefore,as for Cd S/Cd Se core-shell QDs,the thickness of the shell should be well controlled.Compared with classical wide bandgap semiconductor photoanode PEC photodetectors,for the first time this research sensitized photoanode of PEC photodetector devices with Cd S QDs and Cd S/Cd Se core-shell structure QDs,which not only improved absorbance and photogenerated current density of the devices,but also widened their response spectrum and shorten their response time.The results,serving as basis of future research of QDs sensitized PEC photodetectors,would point out one direction for the development of photodetectors. |
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