【作者】 杨旭；

【导师】 曲轶；

【作者基本信息】 长春理工大学 ， 物理电子学， 2013， 博士

【摘要】 伴随着经济的迅速发展,人类对能源的需求量越来越大。而传统能源的日益枯竭促使人们越来越关注新能源的开发与利用。太阳能作为一种环境友好、用之不尽取之不竭的新能源,是最有前途的能源之一。继传统硅太阳电池之后,染料敏化太阳电池以其低廉的成本和简单的制作工艺,为人类有效地利用太阳能提供了新的途径。TiO2光阳极是染料敏化太阳能电池的关键部分,具有吸附染料分子,分离电荷以及传输光生载流子的功能,其性能直接关系到太阳电池的总效率,在染料敏化太阳电池的应用中起到至关重要的作用。因此,开发出高效的光阳极组件是该领域迫切需要解决的热点问题之一。TiO2是一种宽禁带半导体材料,禁带宽度为3.2eV,其新型纳米结构的研究与开发对半导体发光材料、自旋电子学、光催化剂以及染料敏化太阳电池等领域的发展具有重要意义。TiO2纳米晶薄膜是染料敏化太阳电池中最常用也是研究最多的电极材料之一,它是由TiO2晶粒相互连接、贯通组成的三维网状空隙结构,由颗粒与颗粒之间的相互连接来保证电子的传输,但是这种连接是随机的、松散的而且可能存在断点,这就极大地影响了电子在TiO2纳米晶薄膜中的传输过程。而TiO2纳米管薄膜是一种在钛金属表面合成的致密有序的纳米多孔材料,阵列中的管道结构为光生电子提供了传输的高速通道,有利于提高电子的迁移率,在染料敏化太阳电池的阳极应用方面具有很好的发展前景。当前,制备的TiO2纳米管形貌多为直线型,相关研究主要集中在纳米管管长、管径、管壁厚度的有效控制,以及提高TiO2纳米管阵列的表面形貌质量等方面。随着制备方法和制备工艺的不同,TiO2纳米管的外在形貌也在朝着多维结构的方向发展,如两分叉(Y型)、三分叉以及多层分叉的TiO2纳米管阵列等。基于目前TiO2纳米管的成熟技术,并结合染料敏化太阳电池的国内外发展状况,本论文从以下几个方面开展研究：1.在两步阳极氧化法的基础上,考察了生长工艺参数(电解液的组成、温度、氧化电压、氧化时间等)和晶化处理等对TiO2纳米管阵列的影响。同时,总结出一组制备直线型TiO2纳米管阵列材料的最佳工艺参数。为开展Y型TiO2纳米管的研究工作奠定了基础。2.系统地研究了电解液温度对Y型TiO2纳米管阵列形貌的影响,讨论了升温法制备Y型TiO2纳米管的内在机理,并在较宽的温度范围内(20℃-30℃,40℃,50℃,60℃),分别制备出四种Y型TiO2纳米管阵列。当电解液温度设置在40℃以上时,Ti02纳米管阵列顶部将发生过度溶解,出现环状纳米线、管壁破裂以及管长减小等现象,从实际应用的角度来看,不利于保证Y型TiO2纳米管的整体质量。因此,将制备温度控制在20℃-40℃范围内,可以得到较为理想的Y型TiO2纳米管阵列。同时,升温措施还有利于改善TiO2纳米管内部的V型结构,能够进一步扩大下层管径空间,从而提高Y型TiO2纳米管阵列的比表面积。3.采用阳极氧化降压法成功地合成了Y型TiO2纳米管阵列,与升温法制备的样品相比,这种TiO2纳米管阵列具有表面形貌高度规整,Y型纳米管占有率高等特点。同时,本文也对改变氧化电压形成Y型TiO2纳米管的内在机理进行了讨论,并通过进一步扩大降压范围(34V-20V)和两次降压的方式(38V-28V-20V)分别制备出了三分叉TiO2纳米管阵列和两代Y型TiO2纳米管阵列。进一步拓展了TiO2纳米管结构上的多样性。4.采用阳极氧化降压法制备出Y型TiO2纳米管阵列,并通过溶液剥离、白纸提取、多步退火以及TiO2纳米晶浆料配制等工艺,组装成染料敏化Y型TiO2纳米管太阳电池,再利用相同的封装方式制备出染料敏化直线型TiO2纳米管太阳电池。对两种电池进行光电性能测试,通过对比同等膜厚的直/Y型TiO2纳米管太阳电池的开路光电压、短路光电流密度、填充因子以及光电转化效率等性能参数,证明了Y型TiO2纳米管薄膜所组装的电池具有更加优异的光电性能,样品的光电转换效率从2.83%提升至3.35%,效率提高了18.38%。更多还原

【Abstract】 With the increasingly rapid economic growth, global demand for energy is-rising steadily. However, our natural resources are all limited and the traditional energy is becoming less and less, so, more attention has been paid to the development and utilization of new energy. Solar energy is an inexhaustible and environmental benign energy, over the past decades, which has attracted much attention in order to replace the environmentally damaging and diminishing fossil fuels. Up till now, traditional solar cells are made from silicon, due to easy, low cost and environmentally-friendly fabrication. Dye-sensitized solar cell (DSSC) is much cheaper than silicon solar cells. This technology provides a new approach for human to effectively utilize solar energy. TiO2photo-anode is the key component of DSSC which plays an important role in dye loading, electron injection, transportation and collection, etc. it can directly influence on the photoelectric performance of DSSC. Therefore, the development of a high-performance TiO2photo-anode module will become a hotspot in the research of DSSC.TiO2is a wide band-gap compound semiconductor with a direct band gap of3.2eV. The exploration of novel TiO2films has important significance to the development of semiconductor light-emitting materials, spintronics, photocatalysts, dye-sensitized solar cells, etc. TiO2nanocrystalline film is one of the electrode materials for DSSC, the most widely used and most studied, it is made of interconnected TiO2nano-particles with a three-dimensional network structure, which will guarantee the electronic transmission. On the other hand, the connection of TiO2nano-particles in the network structure is random and loose, so that will greatly affect the electron transport properties in the TiO2thin-film. TiO2nanotube arrays, a Ti metal surface preparation of dense and ordered nanoporous materials, its pipeline structure in the arrays can provide a high speed transmission channel for the photo-induced electrons, which will be beneficial for improving the mobility of electrons. Therefore, TiO2nanotube films have great value in the applications of DSSC and a wide developmental foreground. At present, the morphology of TiO2nanotubes are mostly line-shape, the related research mainly focused on the effective control of the nanotube length, diameter, wall thickness, and improving the quality of surface morphology of TiO2nanotube arrays, and so on. As the development of preparation methods and preparation process, the morphology of TiO2nanotubes is developing toward the multi-dimensional structure, such as two-(Y-branched), three-and two-generation Y-branched TiO2nanotube arrays. Based on the domestic and foreign development situation of dye-sensitized solar cells and the advantages of mature TiO2nanotubes fabrication technologies, our thesis is composed of the following contents:1. We discussed the important influence of two-step anodization method to the preparation of highly ordered TiO2nanotube arrays, and analysised of the mutual relations between the growth of TiO2nanotubes and experimental parameters. In the meantime, we also concluded a set of optimal technological parameters for the preparation of line-type TiO2nanotube arrays. All the results will lay a foundation for the design and preparation of Y-branched TiO2nanotube arrays.2. In order to develop the multidimensional structure of TiO2nanotube arrays, Y-branched TiO2nanotube arrays were fabricated on the Ti foil by electrochemical anodic oxidation via increasing the electrolyte temperature. We systematically studied the influence of electrolyte temperature on the morphology characteristics of the Y-branched TiO2nanotubes, and firstly introduced the growth mechanism of Y-branched TiO2nanotubes. Meanwhile, four samples were fabricated by anodic oxidation under different temperature ranges between20℃and60℃. As the results showed that the electrolyte temperature was set at40℃or more in the third step of anodic oxidation, the surface morphology of Y-branched TiO2nanotubes would appear annular nanowires, nanotube nozzle broken or stem nanotube length reduced, etc. That was not conducive to ensuring the overall quality of Y-branched TiO2nanotube arrays. Therefore,20℃～40℃would be the ideal temperature range in the third step during the anodizing process. In addition, we analyzed the effects of electrolyte temperature on the internal structure of Y-branched TiO2nanotubes, the result indicated that as the electrolyte temperature was increased, the V-shaped diameter structure of TiO2nanotubes would be enlarged, the Y-branched TiO2nanotube arrays could obtain a higher surface area.3. We successfully fabricated Y-branched TiO2nanotube arrays by a simplified two-step electrochemical anodic oxidation method via reducing the anodizing voltage. Compared to Y-branched TiO2nanotube arrays prepared by changing electrolyte temperature, this kind of samples have a better surface orderliness and higher occupancy of Y-branched nanotubes. At the meantime, we also illustrated here the synthesis process of Y-branched TiO2nanotubes by reducing the anodizing voltage and a possible growth mechanism. Moreover, to further expand the range of voltage reduction (34V-20V) and reduce the voltage for two times (38V-28V-20V), we obtained the three-branched TiO2nanotubes and two-generation Y-branched TiO2nanotubes, respectively.4. The assembly process of Y-branched TiO2nanotubes photo-anode was introduced here, and a series of different steps for assembly were discussed, such as solution detachment, white paper extraction, multi-step annealing and the preparation of nanocrystalline TiO2 slurry, etc. Then, we measured the photoelectric properties of DSSC assembled with Y-branched TiO2nanotubes, the open voltage, photocurrent density and conversion efficiency was evaluated. Compared to the DSSC assembled with line-shape TiO2nanotubes, we found that Y-branched TiO2nanotube DSSC showed more excellent photoelectric properties, the photoelectric conversion efficiency was increased from2.83%to3.35%, it was enhanced18.38%.更多还原