The Zinc Oxide Nanowires Application To Solar Cells

Dye-sensitized solar cells (DSSCs) are among the most promising low-cost and high-efficiency solar cells with lower production cost compared with traditional sillicon based solar cells. The DSSC is composed of a dye-sensitized and high-surface area TiO2 electrode on a transparent conducting oxide (TCO) and a platinized counter electrode sandwiched together with a I-/I3- redox electrolyte solution. ZnO and TiO2, two wide gap n-type semiconductors with similar energy band, are widely used in dye-sensitized solar cells (DSSCs).ZnO has a strong potential to take over TiO2 for its superior carrier mobility. With simple, low-cost methods, ZnO can be easily grown into various structures, such as nanowires, nanotubes, nanoflowers and nanoparticle films. Among them, highly oriented ZnO nanowires can provide a fast and direct channel for the transport of election in DSSCs and can improve the overall performance greatly.The sensitizer, which captures the sunlight and transfer electron from its oxidation state to the conduction band of anode, is a crucial segment in DSSCs. Although the Ru-based sensitizers have achieved higher performance in DSSCs, the scarcity of Ru and the difficulty in purification set barriers for the commercialization of DSSCs. In addition, the numerous carboxyl groups in Ru-based sensitizer will induce the aggregations of sensitizer on the surface of ZnO, which will deteriorate the performance of DSSCs gradually. D102, with only one carboxyl group on the molecular skeleton, is one of the widely used indoline dyes with higher absorption coefficient than N3, and it can be used as a cheaper alternative in high efficient DSSCs.The fill factor of DSSCs is strongly affected by the semiconductor/electrolyte interface. By coating a thin TiO2 film on the surface of ZnO, the superior conductivity of ZnO and the excellent surface chemistry property of TiO2 can work together to improve the performance of DSSCs.The research of inorganic/organic hybrid solar cells is a hot topic globally in the third generation of solar cells at the present time. Despite various merits such as low cost, the potential of making larger area devices and flexible devices, the development of organic solar cells (polymer or plastic solar cells) are seriously restricted by the poor electronic properties and instability of organic materials. Inorganic/organic hybrid solar cells, combining with the higher absorption of organic materials and the superior conductivity of inorganic materials, are promising in further improving the performance of organic solar cells.Based on the discussions above, the research aeras in this dissertation mainly contain the sections as followed:(1) ZnO with highly c-axis preferred orientation was successfully grown on the ZnO nanoparticles seeded FTO transparent conducting substrate from a hydrothermal method. Characterization methods such as SEM, XRD, PL, FTIR, Raman and Uv-vis are applied to investigate the properties of ZnO nano wires.(2) In the DSSCs herein, platinized FTO and ZnO nanowires sensitized by D102 served as the counter electrode and photoanode respectively, and the LiI/I2 worked as the electrolyte. The FTIR results uncovered the chemical bond between the surface of ZnO and D102. The J-V property of the DSSCs confirmed that the application of ZnO nanowires and D102 improved the photocurrent with joint efforts. The dependence of efficiency on the length of ZnO nanowires was also fundamentally investigated.(3) By the modification of TiCl4, a thin layer TiO2 was formed on the surface of ZnO nanowires to improve the fill factor in DSSCs by the melioration of the semiconductor/electrolyte interface.(4) ZnO:D102/P3HT compound film was prepared and the optical properties were characterized by PL and Uv-vis spectra. The solar cell base on ZnO:D102/P3HT was also fabricated, and in order to improve the overall performance, the efforts needed to make were also concluded, such as the thickness management of different materials, the improvement of circumstance in fabrication and the innovation of the package technology.