Understanding quantum confinement and ligand removal in solution-based ZnO thin films from highly stable nanocrystal ink
Understanding quantum confinement and ligand removal in solution-based ZnO thin films from highly stable nanocrystal ink
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DOI：
10.1039/c8tc01536h
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发表时间：
2018-09-14
影响因子：
6.4
通讯作者：
Swisher, Sarah L.
中科院分区：
文献类型：
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作者：
Sun, Yuhang;Donaldson, Preston D.;Swisher, Sarah L.
我们报告了平均直径为 4 nm 的十二烷硫醇封端纤锌矿 ZnO 纳米晶体的合成过程，该纳米晶体具有单分散性、高溶解性且可稳定保存数月。与以前的 ZnO 墨水配方相比，我们展示了改进的颗粒溶解度和出色的墨水稳定性，从而产生针对印刷电子应用进行优化的 ZnO 纳米晶体墨水。 ZnO 纳米晶体溶液在 341 nm (3.63 eV) 处呈现出吸收峰，这表示相对于本体 ZnO 带隙（大约 3.3 eV）蓝移了大约 0.3 eV。这种蓝移与之前报道的由于量子限制导致带隙增加的模型一致。我们使用变角光谱椭圆光度术（VASE）来确定溶液处理的ZnO纳米晶体薄膜的光学性质，这为了解150-300摄氏度热退火处理期间发生的薄膜成分和形貌的变化提供了有价值的见解。ZnO纳米晶体在沉积成薄膜时保持其量子限制，并且随着热退火温度的升高，量子限制程度逐渐降低。使用红外吸收测量 (FTIR) 和 X 射线光电子能谱 (XPS)，我们发现十二烷硫醇配体在退火过程中从 ZnO 薄膜中去除，从而形成具有极低碳污染的高纯度半导体薄膜。此外，我们表明，300 摄氏度下的退火可以完全去除配体，而晶粒尺寸仅略有增加。采用ZnO纳米晶作为沟道材料并在300℃退火的薄膜晶体管(TFT)表现出中等的迁移率(大约0.002 cm(2) V-1 s(-1))和良好的开/关比>10(4)。这些结果证明了胶体纳米晶体在印刷电子应用中的独特优势：通过控制油墨中纳米晶体的尺寸和表面涂层，可以仔细调整溶液处理薄膜的组成和形态。
We report a synthesis procedure for dodecanethiol capped wurtzite ZnO nanocrystals with an average diameter of 4 nm that are monodisperse, highly soluble, and shelf-stable for many months. Compared to previous ZnO ink recipes, we demonstrate improved particle solubility and excellent ink stability, resulting in ZnO nanocrystal inks that are optimized for printed electronics applications. The ZnO nanocrystal solution exhibits an absorption peak at 341 nm (3.63 eV), which represents a blue-shift of approximately 0.3 eV from the bulk ZnO bandgap (approximate to 3.3 eV). This blue shift is consistent with previously reported models for an increased bandgap due to quantum confinement. We used variable-angle spectroscopic ellipsometry (VASE) to determine the optical properties of solution-processed thin films of ZnO nanocrystals, which provides valuable insight into the changes in film composition and morphology that occur during thermal annealing treatments ranging from 150-300 degrees C. The ZnO nanocrystals maintain their quantum confinement when deposited into a thin film, and the degree of quantum confinement is gradually reduced as the thermal annealing temperature increases. Using infrared absorption measurements (FTIR) and X-ray photoelectron spectroscopy (XPS), we show that the dodecanethiol ligands are removed from the ZnO films during annealing, resulting in a high-purity semiconductor film with very low carbon contamination. Furthermore, we show that annealing at 300 degrees C results in complete ligand removal with only a slight increase in grain size. Thin-film transistors (TFT) using ZnO nanocrystals as the channel material annealed at 300 degrees C show moderate mobility (approximate to 0.002 cm(2) V-1 s(-1)) and good on/off ratio >10(4). These results demonstrate the distinct advantages of colloidal nanocrystals for printed electronics applications: the composition and morphology of the solution-processed film can be carefully tuned by controlling the size and surface coating of the nanocrystals in the ink.