The Fabrication, Interface Modulation Of Of ZnO Nanowires Array And Their Photoelectrical Applications

The arrayed nanostructures are widely used in solar cells to enhance the separation and collectionefficiency of photo-generated carriers due to their abilities to provide the necessary separation interface anddirect pathways for carrier transport. Among them, the wurtzite structured ZnO are considered as one of themost promising functional photoelectric materials due to its lager band gap （3.36eV）, high exciton bindingenergy （⁶0mV） at room temperature, and the excellent mechanical and thermal stability. In the past fewyears, different ZnO nanostructures such as nanowires, nanorods, nanorings and nanotubes are widelystudied in the field of photovoltaic research. However, the fill factor （FF） and the open circuit voltage （Voc）of the ZnO nanostructure based solar cells are still lower than those of their planar counterparts. The lowerFF and Vocindicated the lower charge collection efficiency, which mainly due to the following reasons.Firstly, the poor performances may be due to the low loading amount of quantum dots and poor uniformityfor the traditional sensitization manner. Secondly, there are a lot of surface states and interface statesexisted on the surface of ZnO nanowires array due to the hydrothermal growth manner, which willseriously lower the separation and transport ability of the photo-generated carriers. More importantly, thedisordered ZnO seed layer cannot guarantee its vertical growth along the substrate. The intercrossed ZnOnanowires make it difficult to form an ideal heterojunction for the material filling difficulties into the voidsbetween ZnO nanowires. Aimed to solve the above problems, three parts of research works were carriedout as follows.（1） Synthesis of composite CdS NPs/ZnO NWs nanostructures by the low temperature hydrothermalgrowth combined with the CBD method and their photoelectric properties. Firstly, the ZnOnanowires array was prepared by the low temperatures hydrothermal growth. The composite CdSNPs/ZnO NWs nanostructures was obtained by the deposition of CdS quantum dots onto the surface ofZnO nanowires array through the chemical bath deposition. The I-V measurements showed that thephotocurrent of composite CdS NPs/ZnO NWs nanostructures was about two orders higher than that ofthe pristine ZnO nanowires array. The surface photovoltage spectrum measurements showed the SPSresponses range could be extended to the visible region, which was consistent with their absorption spectrum. In addition, the intensity of the SPS response also increased for the composite CdS NPs/ZnONWs nanostructures. The influences of different CdS deposition times on the SPS responses also wereinvestigated in this section.（2） The fabrication of composition adjustable Zn_xCd_1-xSe@ZnO nanwires array through theion-exchange reactions and their photoelectric properties. The composition adjustableZn_xCd_1-xSe@ZnO core-shell nanwires array was fabricated on FTO glass substrate by the hydrothermalgrowth and the subsequent ion-exchange reaction. The powerful surface photovoltaic spectrummeasurements showed that the SPS response range could be extended to the visible region with thechanging of composition in the shell layer. The type II heterojunction configuration formed betweenthe interface of ZnO nanowire core and the Zn_xCd_1-xSe shell could facilitate the separation andtransportation of photo-generated electron-hole pairs. Therefore, the enhanced SPS response intensitycould be observed for the Zn_xCd_1-xSe@ZnO core-shell nanwires array. The Zn_xCd_1-xSe@ZnOcore-shell nanowires array with different ion-exchange temperature were used as photoanodes forquantum dot sensitized solar cell and the conversion efficiencies in the polysulfidic electrolyte systemwas investigated. In addition, the catalytic activities of three different counter electrodes such as Cu2S,PbS and Cu₂ZnSnS₄were also evaluated. Benefited from the effective electron separation and transferabilities of the type II heterojunction configuration and the high catalytic activity of the novel Cu2Snano-wall structured counter electrode, a photoelectric conversion efficiency of1.70%could beobtained.（3） In-situ growth of ZnO nanowirs array using the nanosphere lithography. In order to furtherimprove the orientation of ZnO nanowire arrays, the highly orientated ZnO seed layer was fabricatedusing magnetron sputtering and ion beam sputtering on the different substrates. The Au nanoholesarray with tunable spaces between the nanoholes was fabricated by using the low-cost and versatilenanosphere lithography technique. Under the limitation of the Au nanoholes, the highly ordered ZnOnanowirs array could be fabricated through the hydrothermal growth, which may be found potentialapplications in the thin film solar cells and other photoelectric devices.