Gopal Ashwini, Hoshino Kazunori, Kim Sunmin, Zhang Xiaojing
Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX 78758, USA.
Nanotechnology. 2009 Jun 10;20(23):235201. doi: 10.1088/0957-4484/20/23/235201. Epub 2009 May 18.
We present a colloidal quantum dot based light emitting diode (QD-LED) which utilizes the p-type silicon substrate as the hole transporting layer. A microcontact printing technique was introduced to pattern self-assembled CdSe/ZnS QD films, which allowed creation of an LED with well-defined geometry suitable for monolithic integration on silicon substrates. Our QD-LED consists of multi-layers of inorganic materials: a combination of Au (thickness: 5 nm) and Ag (12 nm) as the cathode, a ZnO:SnO(2) mixture (ratio 3:1, 40 nm) as the electron transporting layer, CdSe/ZnS QDs as the light emission layer, 1 nm SiO(2) as an energy barrier layer, and p-type silicon as the hole transporting layer. These printed QD-LEDs are capable of multi-color emission peaked at wavelengths of 576 nm, 598 nm, and 622 nm, corresponding to sizes of the embedded QDs with the diameters of 8.4 nm, 9.0 nm, and 9.8 nm respectively. The optimal thickness of the quantum dot layers needed for light emission is characterized using atomic force microscopy: for 8.4 nm QDs, the value is 33 nm (+/- 5 nm) or approximately 4 ML (monolayers). Larger turn on voltages were measured (2, 4 and 5 V) for the smaller average particle diameters (9.8 nm, 9.0 nm and 8.4 nm, respectively). The mixture ratio of Zn and Sn was optimized (40% Zn and 25% Sn) to maintain proper hole-electron recombination at the QD layer and avoid the yellowish-white emission from ZnO/SnO(2).
我们展示了一种基于胶体量子点的发光二极管（QD-LED），它利用p型硅衬底作为空穴传输层。引入了微接触印刷技术来对自组装的CdSe/ZnS量子点薄膜进行图案化处理，这使得能够制造出具有明确几何形状的发光二极管，适合在硅衬底上进行单片集成。我们的QD-LED由多层无机材料组成：Au（厚度：5 nm）和Ag（12 nm）的组合作为阴极，ZnO:SnO₂混合物（比例3:1，40 nm）作为电子传输层，CdSe/ZnS量子点作为发光层，1 nm SiO₂作为能量势垒层，以及p型硅作为空穴传输层。这些印刷的QD-LED能够发出多色光，峰值波长分别为576 nm、598 nm和622 nm，分别对应于直径为8.4 nm、9.0 nm和9.8 nm的嵌入量子点的尺寸。使用原子力显微镜表征了发光所需的量子点层的最佳厚度：对于8.4 nm的量子点，该值为33 nm（±5 nm）或约4个单分子层（单层）。对于较小的平均粒径（分别为9.8 nm、9.0 nm和8.4 nm），测量到的开启电压较高（分别为2 V、4 V和5 V）。优化了Zn和Sn的混合比例（40% Zn和25% Sn），以在量子点层保持适当的空穴-电子复合，并避免ZnO/SnO₂发出黄白色光。
