Department of Chemistry, University of California, Irvine, Irvine, California 92697, USA.
J Am Chem Soc. 2013 Mar 20;135(11):4412-24. doi: 10.1021/ja311974n. Epub 2013 Mar 6.
Iron pyrite (cubic FeS2) is a promising candidate absorber material for earth-abundant thin-film solar cells. Here, we report on phase-pure, large-grain, and uniform polycrystalline pyrite films that are fabricated by solution-phase deposition of an iron(III) acetylacetonate molecular ink followed by sequential annealing in air, H2S, and sulfur gas at temperatures up to 550 °C. Phase and elemental compositions of the films are characterized by conventional and synchrotron X-ray diffraction, Raman spectroscopy, Auger electron spectroscopy, secondary ion mass spectrometry, and X-ray photoelectron spectroscopy (XPS). These solution-deposited films have more oxygen and alkalis, less carbon and hydrogen, and smaller optical band gaps (E(g) = 0.87 ± 0.05 eV) than similar films made by chemical vapor deposition. XPS is used to assess the chemical composition of the film surface before and after exposure to air and immersion in water to remove surface contaminants. Optical measurements of films rich in marcasite (orthorhombic FeS2) show that marcasite has a band gap at least as large as pyrite and that the two polymorphs share similar absorptivity spectra, in excellent agreement with density functional theory models. Regardless of the marcasite and elemental impurity contents, all films show p-type, weakly activated transport with curved Arrhenius plots, a room-temperature resistivity of ~1 Ω cm, and a hole mobility that is too small to measure by Hall effect. This universal electrical behavior strongly suggests that a common defect or a hole-rich surface layer governs the electrical properties of most FeS2 thin films.
黄铁矿（立方晶系 FeS2）是一种很有前途的、富含地球元素的薄膜太阳能电池用吸收材料。在这里，我们报道了一种通过铁(III)乙酰丙酮分子墨水的溶液相沉积，然后在空气、H2S 和硫气中进行顺序退火（温度高达 550°C）而制备的纯相、大晶粒和均匀多晶黄铁矿薄膜。薄膜的相和元素组成通过常规和同步辐射 X 射线衍射、拉曼光谱、俄歇电子能谱、二次离子质谱和 X 射线光电子能谱（XPS）进行了表征。与通过化学气相沉积法制备的类似薄膜相比，这些溶液沉积的薄膜具有更多的氧和碱金属、更少的碳和氢以及更小的光学带隙（E(g) = 0.87 ± 0.05 eV）。XPS 用于评估薄膜表面在暴露于空气和浸入水中以去除表面污染物前后的化学组成。富白铁矿（正交晶系 FeS2）的薄膜的光学测量表明，白铁矿的带隙至少与黄铁矿一样大，并且两种多晶型体具有相似的吸收光谱，这与密度泛函理论模型非常吻合。无论白铁矿和元素杂质含量如何，所有薄膜都表现出 p 型、弱激活的传输，其 Arrhenius 曲线呈弯曲状，室温电阻率约为 1 Ω cm，载流子迁移率太小而无法通过 Hall 效应测量。这种普遍的电性能强烈表明，一种常见的缺陷或富含空穴的表面层控制着大多数 FeS2 薄膜的电性能。
