Hydrothermal Synthesis and Photovoltaic Properties of ZnO Particles and Their Application in TiO_2/ZnO-Based Dye-sensitized Solar Cells

ZnO crystals with different sizes and morphologies were synthesized with different mineralizers(i.e.,hexamethylenetetramine(HMT,(CH2)6N4,99%),urea(CO(NH2)2),and lithium hydroxide(LiOH)) by a hydrothermal method.Their size,morphology and opto-electronic properties were characterized by X-ray diffraction,scanning electron microscopy,UV-Vis diffuse reflectance spectroscopy and surface photovoltage spectroscopy,respectively.The results indicate that the products obtained in the presence of HMT and LiOH are hexagonal wurtzite ZnO particles,and the crystallinity of the product obtained in the presence of CO(NH2)2 is incomplete.The ZnO nanocrystals obtained in the presence of LiOH exhibited a superior photoelectronic response,which could be related to the band-to-band transition and exciton transition.The ZnO crystals obtained were used in dye-sensitized solar cells(DSSCs),as the upper layer of photoanode in TiO2-based DSSCs,showing a light-scattering effect,and the under layer was TiO2 nanocrystal film.In addition,the monolayer ZnO-based DSSCs were also prepared for the comparison purpose.The photoelectronic conversion efficiency of DSSCs was analyzed via the photocurrent-voltage(I-V) curve measurement.It was indicated that the photovoltaic performance of DSSCs with TiO2/ZnO double-layer photoanode was better than that of the monolayer ZnO DSSCs,implying that the light absorption enhancement of DSSCs with a light-scattering layer was due to the incorporation of a greater specific surface area underlayer of the nanocrystalline TiO2and a larger size of ZnO light scattering film.