氧化锌纳米线在太阳电池中的应用研究

【作者】 陈冠雨；

【导师】 陈国荣；

【作者基本信息】 复旦大学 ， 信息功能材料与器件， 2010， 硕士

【摘要】 染料敏化太阳电池与传统的硅太阳电池相比成本更加低廉、效率有望更高。典型的染料敏化太阳电池是由在透明导电基底上的经染料敏化后的纳米结构氧化物作为光阳极,以铂金化的透明导电玻璃作为对电极,中间以含有I-/I3-的溶液作为电解质组成的“三明治”结构。ZnO和TiO2是具有相似的能带结构的宽禁带N型半导体材料,在染料敏化太阳电池中有广泛的应用。ZnO比TiO2具有更高的载流子迁移率,有望能够进一步提高电池的电流特性。ZnO可以制备成多种纳米结构,如纳米线、纳米管、纳米粒子薄膜等。其中,ZnO纳米线具有更好的结晶性能和导电性能,能为电子输运提供直接而快速的通道,可提高太阳电池的电流特性。光敏染料吸收光能并且将激发态电子注入半导体导带中,从而实现光伏转换,是染料敏化太阳电池中的重要组成部分。金属钌配合物系列染料目前已经获得了较高效率,但是金属钉的稀缺以及染料提纯的困难限制了这类染料的实用化发展。并且,钌系列染料分子含有较多羧基致使染料溶液呈酸性,容易在ZnO表面发生团聚导致器件失效。D102是一种纯有机染料,成本低廉,具有较高的光吸收系数,分子骨架上只含有一个羧基,能够大幅度提高基于ZnO纳米线的染料敏化太阳电池效率染料敏化太阳电池的填充因子受半导体/电解液界面的影响。TiO2具有更稳定的表面化学性质,通过制备ZnO/TiO2结构,能够改善半导体电极/电解液界面,同时仍可利用ZnO载流子迁移率高的优点。本文对无机/有机混合型太阳电池也进行了初步研究。有机太阳电池具有制作工艺简单、成本低廉、可制备大面积器件以及制成柔性器件等优点,已经有了广泛研究,但是,由于有机材料的稳定性差以及载流子迁移率较低的影响,纯有机太阳电池能量转换效率很难大幅度提高。无机/有机混合型太阳电池同时利用了有机材料光吸收系数高和无机材料载流子迁移率高的优点,有望提高太阳电池的效率。同时,通过光敏染料敏化无机纳米材料,可以增强器件的光谱响应。基于以上的背景分析,本文工作主要分成以下几个部分：(1)通过水热法,在长有ZnO纳米粒子作为种子层的FTO衬底上生长了垂直于衬底具有高度择优取向的ZnO纳米线,并通过扫描电子显微镜(SEM)、X射线衍射谱(XRD)、荧光光谱(PL)、傅里叶变化红外光谱(FTIR)、Raman光谱和Uv-vis吸收谱等分析测试手段对材料进行了表征。(2)采用经D102敏化的ZnO纳米线作为光阳极,LiI/I2作为电解质,铂金化的FTO玻璃作为对电极组装了染料敏化太阳电池。通过傅里叶变换红外光谱(FTIR)研究了D102与ZnO表面键合的方式。光伏特性测试结果表明,ZnO纳米线的优良导电性以及D102的强吸收共同提高了染料敏化太阳电池的短路电流。同时,比较研究了不同ZnO纳米线长度对太阳电池效率的影响。(3)对ZnO表面通过TiCl4的异丙醇溶液进行处理,生长了一层TiO2薄膜,形成ZnO/TiO2复合材料。通过组装的染料敏化太阳电池表面ZnO/TiO2复合材料能够提高染料敏化太阳电池的填充因子。(4)制备了ZnO:D102/P3HT结构薄膜,通过PL和Uv-vis研究其光学特性。在ZnO:D102/P3HT结构薄膜的基础上制备了无机/有机混合型太阳电池,并对制备高效率混合型太阳电池提出了自己的见解,如薄膜厚度的匹配控制、制备工艺的改善以及后端封装工艺的创新等。更多还原

【Abstract】 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.更多还原