纳米晶尺寸和碳对铜锌硫化锡纳米晶涂层退火过程中晶粒长大的影响,Chemistry of Materials

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纳米晶尺寸和碳对铜锌硫化锡纳米晶涂层退火过程中晶粒长大的影响
Chemistry of Materials ( IF 7.2 ) Pub Date : 2017-02-14 00:00:00 , DOI: 10.1021/acs.chemmater.6b05058
Bryce A. Williams ₁ , Michelle A. Smeaton ₁ , Nancy D. Trejo ₁ , Lorraine F. Francis ₁ , Eray S. Aydil ₁

Affiliation

通过退火由Cu ₂ ZnSnS _4的胶态分散体流延的涂层来制备多晶膜（CZTS）纳米晶体在硫蒸气中。这种基于纳米晶体分散体的途径是用于生产低成本薄膜太阳能电池的有前途的潜在低成本方法。我们研究了纳米晶体尺寸，硫压力和碳浓度对退火过程中微结构发展和晶粒生长的影响。将平均直径为5或35 nm的CZTS纳米晶体的分散体制备的涂层在600℃，50或500 Torr的硫中退火10–60分钟。CZTS纳米晶体的尺寸影响晶粒生长的速率和机理。当退火由5 nm纳米晶体组成的涂层时，异常的晶粒生长会在涂层表面形成微米级的CZTS晶粒。相反，当对由35 nm纳米晶体组成的CZTS涂层进行退火时，晶粒会通过正常的晶粒生长而均匀地生长。晶粒生长速率随硫压力的增加而增加，而与纳米晶体的大小无关。源自用于稳定纳米晶体分散体的配体的碳的存在会增强晶粒的异常生长，但是过多的碳最终会抑制所有晶粒的生长。基于这些观察，我们提出了一种在硫中CZTS纳米晶体涂层退火过程中微观结构发展的机制。尽管人们已经进行了大量研究工作，以期通过配体交换或预退火处理，在硫化或硒化之前从纳米晶体涂层中还原碳，相信降低的碳浓度有助于CZTS微观结构的发展和太阳能电池的效率，但这项工作表明碳在在CZTS晶粒生长中的作用比以前假设的更为复杂和重要：

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Effect of Nanocrystal Size and Carbon on Grain Growth during Annealing of Copper Zinc Tin Sulfide Nanocrystal Coatings

Polycrystalline films were prepared by annealing coatings cast from colloidal dispersions of Cu₂ZnSnS₄ (CZTS) nanocrystals in sulfur vapor. This nanocrystal dispersion-based route is a promising potential low-cost approach for production of low-cost thin-film solar cells. We studied the effects of nanocrystal size, sulfur pressure, and carbon concentration on the microstructure development and grain growth during annealing. Coatings prepared from dispersions of CZTS nanocrystals with an average diameter of either 5 or 35 nm were annealed for 10–60 min at 600 °C in 50 or 500 Torr of sulfur. The CZTS nanocrystal size influenced both the rate and mechanism of grain growth. When coatings composed of 5 nm nanocrystals are annealed, abnormal grain growth forms micrometer-scale CZTS grains on the surface of the coating. In contrast, when CZTS coatings composed of 35 nm nanocrystals are annealed, grains grow uniformly via normal grain growth. Grain growth rates increased with sulfur pressure regardless of the nanocrystal size. The presence of carbon, originating from ligands used to stabilize nanocrystal dispersions, enhances abnormal grain growth, but too much carbon eventually inhibits all grain growth. On the basis of these observations, we propose a mechanism for microstructure development during annealing of CZTS nanocrystal coatings in sulfur. While much research effort has been expended on the reduction of carbon from nanocrystal coatings prior to sulfidation or selenization by means of ligand exchange or preannealing treatments in the belief that reduced carbon concentration aids CZTS microstructure development and solar cell efficiencies, this work indicates that carbon plays a more complex and significant role in CZTS grain growth than previously assumed: carbon may be beneficial or even required for rapid grain growth during sulfidation.

更新日期：2017-02-14

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