The Designs And Multi-functional Applications Of ZnO-based Photodetectors

As the basis of optoelectronic information technology,photodetection technology plays a vital role in the information age and has gained tremendous attention and rapid development worldwide,which has a wide range of applications in areas such as image sensing,flame detection,pollution surveillance,medical and health monitoring and energy exploration.Nowadays,it is increasingly difficult for the traditional photodetectors to meet the diversified needs.For example,one of the hotspots of the optoelectronics is flexible and wearable electronic device,whereas the traditional photodetectors are usually fabricated in rigid substrates.Furthermore,the traditional photodetectors are poorly compatible with flexible technologies.For another,ultraviolet(UV) photodetectors are the key technologies in UV warning systems in military fields.However,expensive filters are usually needed for specific band photodetection.Moreover,deep ultraviolet photodetectors with high performance are limited by the synthesis of wide band gap semiconductors with high quality.As one of the next-generation wide bandgap semiconductor materials,zinc oxide(ZnO) has wide application prospects in optoelectronics.This dissertation was finished based on ZnO and ZnO-based nanomaterials and their applications in photodetection.First of all,a fiber-shaped photodetector based on ZnO nanowire network was constructed for omnidirectional photodetecting.Moreover,CsPbBr₃ perovskite nanosheets were used to broaden the response band of the ZnO based photodetectors with flexibility.And deep UV light detection was realized by a photodetector based on Zn₂SnO₄,which is prepared via alloying ZnO and SnO₂.Graphene was then introduced to improve the photoelectric properties of the device.The main research results are summarized as follows,(1)ZnO nanowire network-based fiber-shaped omnidirectional UV photodetector.Firstly,the ZnO nanowire network-based photodetector was constructed by a vacuum filtration transfer method,the photodetector exhibited superior photoelectric properties(a low dark current of 7.73 nA,a high on/off ratio of 3.9×10³) and the capability of imaging.The fiber-shaped omnidirectional UV photodetector was fabricated using a KEVLAR wire as the substrate.Benefitting from the good mechanical capacity,the fiber-shaped photodetector worked normally(the photocurrents were 40?A) when bent at different angles,showing good flexible stability.For incident light from different angles,the photodetector has almost the same responsivities indicating omnidirectional photodetection.The construction of the ZnO nanowire network omnidirectional photodetector provides a new idea for flexible fiber-shaped photodetection.(2)ZnO nanowires/CsPbBr₃ nanosheets flexible photodetector for broadband detection.The ultrathin CsPbBr₃ nanosheets were synthesized at room temperature with a thickness of 8nm.Both of the ZnO nanowires and CsPbBr₃ nanosheets were transferred onto a PET substrate for the construction of the flexible photodetector.And the photoelectric properties of the device were first measured under bending state,no change in photocurrent was observed,which points out exceptional flexibility.Then the photoelectric properties of the device were studied under illumination of ultraviolet and visible light,respectively.A large on/off ratio(>10³) and a high detectivity(10¹² Jones)of the device were gained under illumination of 320 nm and 532nm.The proposed construction strategy for highly flexible and performance-integrated PDs shows great potential in future smart,wearable optoelectronic devices.(3)Zn₂SnO₄ nanocrystalline UV-B photodetector.The Zn₂SnO₄ nanocrystalline with high crystallinity and purity were synthesized by laser ablation in liquid(LAL) and hydrothermal methods.The mechanism in the LAL process was studied.And the growth mechanism of the Zn₂SnO₄ nanocrystalline was discussed based on samples grown under different temperatures and time by the hydrothermal method.The Zn₂SnO₄ nanocrystalline based photodetector with a smooth and dense surface was constructed by centrifugal-casting.Compared with ZnO nanomaterial,the prepared Zn₂SnO₄ nanocrystalline has a larger bandgap up to 3.9 eV,which corresponds to UV-B light.The Zn₂SnO₄ nanocrystalline photodetector has a peak responsivity at 325 nm and a high on/off ratio(>10³),which can be retained after 10000 s of testing.In addition,the Zn₂SnO₄ nanocrystalline-based photodetector has a higher photocurrent compared with the Zn₂SnO₄ nanomaterials prepared by the hydrothermal method.The ZnO-based ternary oxides with a large bandgap have a promising prospect in deep ultraviolet photodetection.(4)Zn₂SnO₄ nanocrystalline/graphene ultraviolet photodetector with fast response.Graphene was introduced to the Zn₂SnO₄ nanocrystalline photodetector for the improvement of photoelectric properties.After introducing graphene,the bandgap and the crystal structure of Zn₂SnO₄ nanocrystalline remained unchanged.In addition,corresponding device has better photoelectric properties,the photocurrent was improved from 0.31?A to 0.49?A.In addition,the time constant were reduced by 20 times while the bandwidth response range was enlarged from 280 Hz to 1200 Hz.The results show that the introduction of graphene provides a feasible strategy for improving the photoelectronic device.