TiO₂ Heterojunction Nanostructures Based Photodetector: Fabrication And Photoelectric Performance

Photodetector is a device that can convert incident optical signal into electric signal.In recent years,it has wide applications in image sensing,optical communication and environmental monitoring.So far,abundant photodetectors based on single TiO₂ have been reported.However,these photodetectors have some limitations in performance.Therefore,this dissertation proposes the construction of heterojunction nanostructures instead of single TiO₂ to improve device performance.Heterojunction photodetectors not only display the advantages of individual component,but also exhibit novel properties.This dissertation designs two photodetectors based on TiO₂ combined with ZnO and perovskite,respectively.The contents of the research are described as follows:?1?Zn O not only possesses an appropriate band gap,but also has good stability and strong absorbance in the UV light region.However,photodetectors based on ZnO also suffer from several shortcomings.For example,they have low responsivity and photocurrent.Besides,the rise and decay times reach up to tens even hundreds of seconds.By utilizing electrospinning technology,one-dimensional aligned ZnO nanofibers are obtained and the Li element is successfully doped into the nanofibers.By changing electrospinning time?5,10,15 and 20 min?,it is concluded that the optimum electrospinning time for ZnO and Li doped ZnO is 10 min.By employing atomic layer deposition technology?ALD?,the TiO₂ thin film of different thickness?1,3 and 7 nm?is deposited on the surface of Li:ZnO-10.The Li:ZnO-10/TiO₂-3?the thickness of TiO₂ thin film is 3 nm?exhibits optimal performance,with the photocurrent of 36.8?A under white light illumination.And the rise and decay time is 7.52 and 30.20 s,respectively.The responsivity is 15.8 A W^-1under irradidation of 340 nm monochromatic light,which is52.6 and 31.6 times higher than that of ZnO and Li:ZnO,respectively.The heterojunction of Li:ZnO and TiO₂ can efficiently reduce the recombination of photogenerated electron-hole pairs and accelerate their separation and transporation.?2?The inorganic semiconductor based nanoscale photodetectors suffer from some shortcomings of slow response speed and narrow response range.Recently,the organic-inorganic perovskite material exhibits excellent properties,which is regarded as a promising material to construct photodetectors.So,by integrating TiO₂ with perovskite into heterojunction,high-performance photodetectors would be obtained.TiO₂ and CdS are synthesized by convenient hydrothermal and successive ion layer absorption and reaction methods?SILAR?,respectively.The perovskite layer is fabricated by spin coating method.The structure is self-powered.By optimizing the reaction cycles of CdS,the sample with 20 cycles exhibits the best performance.Furthermore,P3 HT layer is added on the structure in order to decrease the dark current of TiO₂/CdS-20cycles/perovskite.The responsivity of TiO₂/CdS-20 cycles/perovskite/P3 HT is 6 A W^-1.Besides,under the illumination of 730 nm monochromatic light,its on/off ratio,rise time and decay time are 135.37,6.56 s and 3.70 s,respectively.The fantastic performance is attributed to the strong materials' light absorbance ability,unique morphology and the matching band energy.The photodetector based on single TiO₂ has the shortcomings of low photocurrent and slow response speed.In this dissertation,heterojunction structures based photodetectors were constructed by integrating TiO₂ with ZnO and perovskite,respectively,which exhibit enhanced optoelectronic performance.