Sudies Of Photoelectric Properties Of1D ZnO Nanomaterials And The Applications For Devices

ZnO is a direct wide band-gap semiconductor, and the band-gap is about3.37eV at room temperature. It naturally exhibits the electrical property of n-type semiconductors, and usually has a hexagonal wurtzite structure.The nano-effects greatly enhance the photoelectric properties of one-dimensional (1D) ZnO nanomaterials, which makes them have promising potential applications in the field of solar cells, ultraviolet (UV) photodetection and photoelectrochemical (PEC) water splitting.1D ZnO nanomaterials with different morphologies were synthesized via hydrothermal synthesis and chemical vapor deposition (CVD), and their mechanism of self-powered photoelectric response was deeply investiaged. The effects of photosensitizers, such as ZnIn2S4and CdS, on the PEC performance of ID ZnO nanomaterials were also systematically studied on this basis.ZnO nanowire arrays (NWAs) and ZnO nanowires were synthesized by hydrothermal synthesis and CVD. The as-grown1D ZnO nanomaterials have a hexagonal wurtzite structure, a growth direction of [0001], good crystallinity and low crystal defects. The electron concentration and carrier mobility of one single ZnO nanowire synthesized by CVD method were calculated experimentally and numerically to be1.06×1017cm-3and1.68cm2V-1s-1, respectively.The self-powered photosensing performance of a heterojunction based on a single ZnO nanowire and a p-type Si film was studied. The heterojunction showed obvious rectification characteristics, and had a rectification ratio of103. According to the thermionic emission theory, the ideal factor of the heterojunction was estimated to be2. The device showed photoresponse to both UV and visible light at reverse bias, and only had response to UV light at forward bias. At zero bias, it had a photosensitivity of2×104to UV light and5×103to visible light, and the response time was about7.4ms. The photocurrent at zero bias and the open-circuit voltage showed square root and logarithmical dependences on the light intensity, respectively.The self-powered photodetecting performance of ZnO NW networks and ZnO NWAs was also investigated. A Schottky junction between ZnO NW networks and a Pt electrode had a sensitivity of800to UV light. A Pt/ZnO NWAs/Pt self-powered UV detector was fabricated, and the difference between the Schottky barrier heights at the two ends of the device induced the self-powered phenomenon. When the difference was30meV, the sensitivity to UV light reached to475. The effects of temperature on the performance of the Al/ZnO NWAs/Pt Schottky type self-powered photodetectors were also explored. Under340K, the photocurrent increased with the rising of temperature. As temperature was increased successively, the photocurrent decreased. Above420K, the electrode was oxidized and the device was damaged.The PEC performance of ZnO NWAs/RGO/ZnIn2S4heterostructure was studied. The as-grown ZnIn2S4had a hexagonal cryatal structure. After reduction process, the oxygen content of RGO decreased to27%. After combination with RGO and ZnIn2S4, the heterostructure showed enhanced visible absorption. The photo-to-hydrogen efficiency of ZnO NWAs/RGO/ZnIn2S4heterojunction reached to0.46%, which was twice that of pure ZnO NWAs. The introduction of RGO enlarges the surface area of the photoanode and promotes photogenerated carriers transport between ZnO and ZnIn2S4. Besides, ZnIn2S4enhances the visable light absorption efficiency of the photoanode, and then improves its photo-to-hydrogen efficiency.The PEC properties of3D branched ZnO/CdS composites were investigated. Compared with the pure ZnO NWAs, the3D branched ZnO/CdS composites had a much higher conversion efficiency of1.62%. The3D branched nanostructure of ZnO NWAs has an improved roughness factor and an enhanced surface area, which contributes to the increase in light absorption and the transfer of charge carriers at the solid/liquid interfaces. Meanwhile, the introduction of CdS greatly enhances the photocatalytic activity of the photoanode in visible region, and the space electric field between CdS and ZnO accelerates the separation of photogenerated carriers. In addition, the photocorrosion problems of3D branched ZnO/CdS composites were also explored. A TiO2protective layer was deposited onto the photoande using the ALD method to improve the PEC stability.