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首页> 外文学位 >Synthesis, Deposition, and Microstructure Development of Thin Films Formed by Sulfidation and Selenization of Copper Zinc Tin Sulfide Nanocrystals.
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Synthesis, Deposition, and Microstructure Development of Thin Films Formed by Sulfidation and Selenization of Copper Zinc Tin Sulfide Nanocrystals.

机译：铜锌硫化锡纳米晶体的硫化和硒化形成的薄膜的合成，沉积和微观结构发展。

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摘要

Significant reduction in greenhouse gas emission and pollution associated with the global power demand can be accomplished by supplying tens-of-terawatts of power with solar cell technologies. No one solar cell material currently on the market is poised to meet this challenge due to issues such as manufacturing cost, material shortage, or material toxicity. For this reason, there is increasing interest in efficient light-absorbing materials that are comprised of abundant and non-toxic elements for thin film solar cell. Among these materials are copper zinc tin sulfide (Cu2ZnSnS4, or CZTS), copper zinc tin selenide (Cu2ZnSnSe4, or CZTSe), and copper zinc tin sulfoselenide alloys [Cu2ZnSn(SxSe1-x )4, or CZTSSe]. Laboratory power conversion efficiencies of CZTSSe-based solar cells have risen to almost 13% in less than three decades of research.;Meeting the terawatt challenge will also require low cost fabrication. CZTSSe thin films from annealed colloidal nanocrystal coatings is an example of solution-based methods that can reduce manufacturing costs through advantages such as high throughput, high material utilization, and low capital expenses. The film microstructure and grain size affects the solar cell performance. To realize low cost commercial production and high efficiencies of CZTSSe-based solar cells, it is necessary to understand the fundamental factors that affect crystal growth and microstructure evolution during CZTSSe annealing.;Cu2ZnSnS4 (CZTS) nanocrystals were synthesized via thermolysis of single-source cation and sulfur precursors copper, zinc and tin diethyldithiocarbamates. The average nanocrystal size could be tuned between 2 nm and 40 nm, by varying the synthesis temperature between 150 °C and 340 °C. The synthesis is rapid and is completed in less than 10 minutes. Characterization by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy confirm that the nanocrystals are nominally stoichiometric kesterite CZTS. The ~2 nm nanocrystals synthesized at 150 °C exhibit quantum confinement, with a band gap of 1.67 eV. Larger nanocrystals have the expected bulk CZTS band gap of 1.5 eV. Several micron thick films deposited by drop casting colloidal dispersions of ~40 nm CZTS nanocrystals were crack-free, while those cast using 5 nm nanocrystals had micron-scale cracks. We showed the applicability of these nanocrystal coatings for thin film solar cells by demonstrating a CZTS thin film solar cell using coatings annealed in a sulfur atmosphere.;We conducted a systematic study of the factors controlling crystal growth and microstructure development during sulfidation annealing of films cast from colloidal dispersions of CZTS nanocrystals. The film microstructure is controlled by concurrent normal and abnormal grain growth. At 600 °C to 800 °C and low sulfur pressures (50 Torr), abnormal CZTS grains up to 10 microm in size grow on the surface of the CZTS nanocrystal film via transport of material from the nanocrystals to the abnormal grains. Meanwhile, the nanocrystals coarsen, sinter, and undergo normal grain growth. The driving force for abnormal grain growth is the reduction in total energy associated with the high surface area nanocrystals. The eventual coarsening of the CZTS nanocrystals reduces the driving force for abnormal crystal growth. Increasing the sulfur pressure by an order of magnitude to 500 Torr accelerates both normal and abnormal crystal growth though sufficient acceleration of the former eventually reduces the latter by reducing the driving force for abnormal grain growth. For example, at high temperatures (700-800 oC) and sulfur pressures (500 Torr) normal grains quickly grow to ~500 nm which significantly reduces abnormal grain growth. The use of soda lime glass as the substrate, instead of quartz, accelerates normal grain growth. Normal grains grow to ~500 nm at lower temperatures and sulfur pressures (i.e., 600 °C and 50 Torr) than those required to grow the same size grains on quartz (700 °C and 500 Torr). Moreover, carbon is removed by volatilization from films where normal crystal growth is fast.;There are significant differences in the chemistry and in the thermodynamics involved during selenization and sulfidation of CZTS colloidal nanocrystal coatings to form CZTSSe or CZTS thin films, respectively. To understand these differences, the roles of vapor pressure, annealing temperature, and heating rate in the formation of different microstructures of CZTSSe films were investigated. Selenization produced a bi-layer microstructure where a large CZTSSe-crystal layer grew on top of a nanocrystalline carbon-rich bottom layer. Differences in the chemistry of carbon and selenium and that of carbon and sulfur account for this segregation of carbon during selenization. For example, CSe 2 and CS2, both volatile species, may form as a result of chalcogen interactions with carbon during annealing. Unlike CS2, however, CSe2 may readily polymerize at room temperature and one atmosphere. Carbon segregation may be occurring only during selenization due to the formation of a Cu-Se polymer [i.e., (CSe 2-x)] within the nanocrystal film. The (CSe2-x) inhibits sintering of nanocrystals in the bottom layer. Additionally, a fast heating rate results in temperature variations that lead to transient condensation of selenium on the film. This is observed only during selenization because the equilibrium vapor pressure of selenium is lower than that of sulfur. The presence of liquid selenium during sintering accelerates coarsening and densification of the normal crystal layer (no abnormal crystal layer) by liquid phase sintering. Carbon segregation does not occur where liquid selenium was present.
机译：通过向太阳能电池技术提供数十兆瓦的电力，可以显着减少与全球电力需求相关的温室气体排放和污染。由于制造成本，材料短缺或材料毒性等问题，目前市场上没有一种太阳能电池材料准备好应对这一挑战。因此，对于由薄膜太阳能电池的由丰富且无毒的元素组成的有效的光吸收材料引起了越来越多的关注。在这些材料中，有硫化铜锌锡（Cu2ZnSnS4或CZTS），硒化铜锌锡（Cu2ZnSnSe4或CZTSe）和硫化锌铜锌锡硒合金[Cu2ZnSn（SxSe1-x）4或CZTSSe]。在不到三十年的研究中，基于CZTSSe的太阳能电池的实验室电源转换效率已经提高到近13％。要应对兆瓦的挑战，还需要低成本的制造方法。来自退火的胶态纳米晶体涂层的CZTSSe薄膜是基于溶液的方法的一个示例，该方法可以通过诸如高产量，高材料利用率和低资本支出的优势降低制造成本。膜的微观结构和晶粒尺寸影响太阳能电池的性能。为了实现基于CZTSSe的太阳能电池的低成本商业化生产和高效率，有必要了解影响CZTSSe退火过程中影响晶体生长和微观结构演变的基本因素。;通过单源阳离子的热解合成了Cu2ZnSnS4（CZTS）纳米晶体。和硫前体铜，锌和二乙基二硫代氨基甲酸锡。通过在150°C至340°C之间改变合成温度，可以将平均纳米晶体尺寸调整在2 nm至40 nm之间。合成快速并且在不到10分钟的时间内完成。通过X射线衍射，拉曼光谱，透射电子显微镜和能量色散X射线光谱进行的表征证实，纳米晶体是名义上化学计量的钾钛矿CZTS。在150°C下合成的〜2 nm纳米晶体表现出量子限制，带隙为1.67 eV。较大的纳米晶体的预期CZTS体带隙为1.5 eV。通过滴铸约40 nm CZTS纳米晶体的胶态分散体而沉积的几微米厚的膜无裂纹，而使用5 nm纳米晶体流延的膜具有微米级的裂纹。通过演示在硫气氛中退火的涂层来演示CZTS薄膜太阳能电池，我们证明了这些纳米晶体涂层在薄膜太阳能电池中的适用性;我们对铸塑薄膜的硫化退火过程中控制晶体生长和微观结构发展的因素进行了系统研究从CZTS纳米晶体的胶体分散体中提取。薄膜的微观结构受正常和异常晶粒长大的控制。在600°C至800°C和低硫压（50托）下，通过将材料从纳米晶体传输到异常晶粒，最大尺寸为10微米的异常CZTS晶粒生长在CZTS纳米晶体膜的表面上。同时，纳米晶体变粗，烧结并经历正常的晶粒生长。异常晶粒生长的驱动力是与高表面积纳米晶体相关的总能量的减少。 CZTS纳米晶体的最终粗化降低了异常晶体生长的驱动力。将硫压增加一个数量级至500 Torr可以加速正常和异常晶体的生长，尽管前者的足够加速度最终会通过减小异常晶粒生长的驱动力最终降低后者。例如，在高温（700-800 oC）和硫压力（500 Torr）下，正常晶粒会迅速生长到〜500 nm，这大大减少了异常晶粒的生长。使用钠钙玻璃代替石英代替硅，可促进正常晶粒的生长。普通晶粒的生长温度和硫压（即600°C和50 Torr）比在石英上生长相同尺寸的晶粒（700°C和500 Torr）所需的温度和硫压力低（〜500 nm）。此外，在正常晶体生长较快的薄膜中，碳会通过挥发作用被除去。在CZTS胶态纳米晶体涂层的硒化和硫化过程中，化学和热力学存在显着差异，分别形成CZTSSe或CZTS薄膜。为了理解这些差异，研究了蒸气压，退火温度和加热速率在形成CZTSSe薄膜不同微结构中的作用。硒化产生了双层微观结构，其中大的CZTSSe晶体层生长在纳米晶富含碳的底层的顶部。碳和硒的化学差异以及碳和硫的化学差异解释了硒化过程中碳的这种偏析。例如，CSe 2和CS2都是挥发性物质，可能是由于硫族元素在退火过程中与碳相互作用而形成的。但是，与CS2不同，CSe2可以在室温和一个大气压下容易聚合。由于在纳米晶体膜中形成了Cu-Se聚合物[即（CSe 2-x）]，所以仅在硒化期间可能发生碳偏析。 （CSe2-x）抑制了底层中纳米晶体的烧结。另外，快速的加热速率会导致温度变化，从而导致硒在薄膜上短暂凝结。由于硒的平衡蒸气压低于硫的平衡蒸气压，因此只能在硒化期间观察到。烧结过程中液态硒的存在通过液相烧结促进了正常晶体层（无异常晶体层）的粗化和致密化。存在液态硒的地方不会发生碳偏析。

著录项

  • 作者

    Chernomordik, Boris David.;

  • 作者单位

    University of Minnesota.;

  • 授予单位 University of Minnesota.;
  • 学科 Engineering Chemical.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2014
  • 页码 183 p.
  • 总页数 183
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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