Abstract In this study, a sputtering system was adopted for the preparation of Cu2ZnSnS4 (CZTS) thin films with high material quality. The system precisely controlled the elemental ratio in a copper-zinc-tin (CZT) precursor for contributing to the grain growth of CZTS crystallites, and reduced the detrimental formation of the Cu2-xS secondary phase during the high-temperature sulfurization process. The CZT precursor was prepared in a layer sequence of Zn/Sn/Cu/Zn, as the Cu-capping layer could protect the underlying Zn/Sn bilayer from volatilization during the high-temperature sulfurization. The CZT precursors were subjected to the sulfurization process at varied temperatures ranging from 480 to 560 °C for 20 min to form the CZTS thin film. In this study, the Cu/(Zn + Sn) and Zn/Sn ratios in the CZTS film were studied by energy dispersive X-ray spectroscopy measurements, and both ratios revealed elevations with an increasing sulfurization temperature, owing to the thermal volatilization of Zn and Sn. Thus, the formation of the undesirable Cu2-xS secondary phase was enhanced, and the surface roughness and density of voids on the CZTS thin films were increased. For a reduced Zn/Sn ratio with a reduced sulfurization temperature, the improved CZTS thin-film quality was demonstrated by the increased X-ray diffraction (XRD) and Raman intensity, along with the reduction of the XRD linewidth of the (112) CZTS crystal phase. A CZTS thin film with a sulfurization condition of 500 °C for 20 min showed a low Zn/Sn ratio (at 1.1), along with the features of a dense and smooth thin-film surface. Moreover, a reduced photoluminescence spectra full width at half maximum (FWHM) value of 92.7 meV was observed. In addition, for further improving the grain growth of CZTS, a pre-annealing process of a CZT precursor was conducted at a temperature of 350 °C for 30 min. An enhancement of the CZTS crystallite size with the stoichiometric formation of a CZTS phase and a reduced Cu2-XS phase was observed, indicating the superior material quality of the CZTS thin films.

中文翻译：

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通过减少Cu2-xS第二相提高CZTS薄膜材料质量的Zn/Sn比研究

摘要 本研究采用溅射系统制备高品质Cu2ZnSnS4 (CZTS)薄膜。该系统精确控制了铜-锌-锡 (CZT) 前驱体中的元素比例，以促进 CZTS 晶粒的晶粒生长，并减少了高温硫化过程中 Cu2-xS 二次相的有害形成。CZT 前驱体按 Zn/Sn/Cu/Zn 的层序制备，因为 Cu 覆盖层可以保护下面的 Zn/Sn 双层在高温硫化过程中不挥发。CZT 前驱体在 480 至 560°C 的不同温度下进行硫化过程 20 分钟，以形成 CZTS 薄膜。在这项研究中，通过能量色散 X 射线光谱测量研究了 CZTS 薄膜中的 Cu/（Zn + Sn）和 Zn/Sn 比率，由于 Zn 和 Sn 的热挥发，这两个比率都显示出随着硫化温度的升高而升高。因此，不希望有的 Cu2-xS 二次相的形成得到加强，CZTS 薄膜上的表面粗糙度和空隙密度增加。对于随硫化温度降低而降低的 Zn/Sn 比，通过增加的 X 射线衍射 (XRD) 和拉曼强度以及 (112) CZTS 的 XRD 线宽的减少证明了 CZTS 薄膜质量的提高晶相。硫化条件为 500 °C 20 分钟的 CZTS 薄膜显示出低 Zn/Sn 比（1.1），以及致密且光滑的薄膜表面特征。而且，观察到减少的光致发光光谱半峰全宽 (FWHM) 值为 92.7 meV。此外，为了进一步改善 CZTS 的晶粒生长，在 350°C 的温度下进行了 CZT 前驱体的预退火过程 30 分钟。观察到 CZTS 微晶尺寸随着 CZTS 相的化学计量形成和 Cu2-XS 相的减少而增加，表明 CZTS 薄膜具有优异的材料质量。