ACT/SGER: Metastable Titania-Germanium (Ti02-Ge) Nanocomposites for Photovoltaic Applications

纳米结构二氧化钛（TiO2）具有稳定性、化学惰性、成本低等优点，是一种很有前途的光伏半导体材料。二氧化钛的光隙为3.2 eV，位于太阳光谱的紫外区。然而，太阳光谱的峰值是在可见光区。因此，为了提高光伏工艺的效率，通过各种方法定制二氧化钛纳米颗粒，使其在可见光下有用。我们建议研究一种新的纳米结构材料——钛锗，它将成为染料敏化二氧化钛的稳定替代品。我们将使用已经成熟的沉积技术，例如溅射和金属有机化学气相沉积，来合成样品。利用透射电子显微镜对复合材料样品进行了选择面积衍射分析，发现锗纳米团簇（量子点）在二氧化钛基体中均匀分布。与二氧化钛相比，氧化锗相对较高的形成热促进了元素锗纳米点的形成。锗纳米点的大小将通过控制退火技术在薄膜厚度上进行调制。这种尺寸变化将允许利用量子点尺寸相关的锗纳米点带隙变化来敏化二氧化钛并改善其光伏性能。数学和物理科学理事会的反恐方法项目支持基础研究和劳动力发展方面的新概念，这些新概念有可能为国家安全做出贡献。为了打击扩散和隐藏的恐怖活动，显然需要自供电的便携式设备。为此，太阳能发电是一种理想的可再生能源。目前，晶体或非晶硅太阳能电池将太阳能转化为可用电力的效率可能高达20-30%，甚至可以商业化生产。晶体硅受到制造过程的复杂性的困扰，而相对便宜的非晶硅（a- si）光伏电池具有光诱导光伏性能退化的基本缺点。我们建议研究一种新的稳定的光伏材料钛锗。二氧化钛只吸收太阳能中的高能紫外线成分。由于大部分太阳光线在可见光范围内，已经设计了几种方案来克服这一限制。制备钛锗纳米复合材料是一种诱导二氧化钛吸收可见光的新方法。锗起吸收光的作用。在体积形式中，锗只吸收太阳能的红外部分。通过形成纳米尺寸的锗团簇，也称为纳米点，Ge的吸收特性可以从红外到可见光变化，从而提高钛-锗纳米复合材料的太阳能吸收效率。制造这种材料需要使用已经发展起来的技术。该研究包括二氧化钛-锗纳米复合材料的制备，其完整的结构和电子表征，以及其光伏性能的研究。

Nanostructured titania (TiO2) is a promising semiconductor for photovoltaic applications due to its stability, chemical inertness, cost, etc. The optical gap of titania is 3.2 eV that lies in the ultraviolet region of the solar spectrum. However, the peak of the solar spectrum is in the visible region. Therefore, to increase the efficiency of the photovoltaic processes, titania nanoparticles are customized by various methods in order to make them useful in the visible light. We propose to study a new nanostructured material, titania-germanium which will be a stable alternative to dye sensitized titania. We will use already mature deposition techniques, e.g. sputtering and metallorganic chemical vapor deposition, to synthesize the samples. Preliminary experiments of composite samples using selected area diffraction analyses in a transmission electron microscope showed uniform distribution of germanium nanoclusters (quantum dots) in the titania matrix. The formation of elemental germanium nanodots is facilitated by the relatively higher heat of formation of germanium oxide, compared to that of titania. The size of the germanium nanodots will be modulated across the thickness of the thin films by controlled annealing techniques. Such size variation will allow the possibility to use quantum dot size related change in the bandgap of germanium nanodots to sensitize titania and improve its photovoltaic properties. The Approaches to Combat Terrorism Program in the Directorate for Mathematics and Physical Sciences supports new concepts in basic research and workforce development with the potential to contribute to national security. To combat diffused and hidden terrorist activities, there is an obvious need for self-powered portable devices. For this purpose, solar electric power is an ideal renewable energy source. Currently, crystalline or amorphous silicon solar cells with efficiency to convert solar power to usable electricity as high as 20-30% are possible and even commercially produce. Crystalline silicon suffers from the complexity of the fabrication process where as relatively inexpensive amorphous silicon (a-Si) photovoltaics have a fundamental drawback of light induced degradation of photovoltaic properties. We propose to study a new stable material titania-germanium for photovoltaic applications. Titania absorbs only high-energy ultraviolet component of solar energy. Several schemes have been devised to overcome this limitation since the majority of the solar light is in the visible range. Forming titania-germanium nanocomposite is a new method of inducing visible light absorption in titania. Germanium serves as the light absorber. Ge, in the bulk form, absorbs only the infrared component of the solar energy. By forming nanometer size germanium clusters, also known as nanodots, the absorption properties of Ge can be varied from infrared to visible, thereby improving the solar light absorption efficiency of the titania-germanium nanocomposite. Fabrication of such materials will require the use of techniques that are already developed. The proposed study includes the fabrication of TiO2-Ge nanocomposite, its complete structural and electronic characterization, and investigation of its photovoltaic properties.