Simulation for forming uniform inkjet-printed quantum dot layer
Simulation for forming uniform inkjet-printed quantum dot layer
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DOI：
10.1063/1.5079863
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发表时间：
2019-02-14
影响因子：
3.2
通讯作者：
Lee, Changhee
中科院分区：
文献类型：
--
作者：
Park, Yubin;Park, Yeseul;Lee, Changhee
量子点（QD）发光二极管具有发光波长可调、带宽窄等优点，已成为下一代显示技术的候选器件之一。对于QD像素图案化，喷墨印刷在材料损失和处理时间方面优于其他方法。然而，喷墨印刷难以控制QD层的均匀性。考虑到QD层的适当厚度和均匀性是显示器中高效率的重要因素，这是一个严重的问题。这个问题背后的主要原因是已知的咖啡环效应（CRE），其中跨固着液滴的差异蒸发导致内部流体的边缘流动，并导致悬浮的QD集中在液滴的周边。在这里，证明了通过降低CRE来改善层均匀性的可能性。采用数值求解偏微分方程的方法，对量子点胶体溶液液滴的蒸发过程进行了数学模拟。利用Navier-Stokes方程、连续性条件和蒸发通量等物理参数的数学表达式建立偏微分方程，并采用有限差分法进行求解。过滤器被包括在该过程中，以抑制不必要的不稳定性。利用该模拟方法，通过观察各参数随时间的变化，分析了整个蒸发过程。结果发现，降低CRE的各种条件：足够的初始浓度，适当的溶剂类型，小的接触角，和快速的蒸发速率。结果似乎与实验数据一致。由AIP Publishing授权出版。
The quantum dot (QD) light emitting diode has emerged as one of the candidates for the next generation display technology with advantages such as tunable wavelength of emitted light and narrow bandwidth. For QD pixel patterning, inkjet-printing is superior to other methods in terms of material loss and process time. However, inkjet-printing has difficulty in controlling the uniformity of the QD layer. This is a serious issue considering that proper thickness and uniformity of the QD layer are important factors for high efficiency in displays. The main reason behind this problem is known to be the coffee ring effect (CRE), in which differential evaporation across a sessile droplet leads to an edge-ward flow of the fluid inside and causes suspending QDs to be concentrated at the perimeter of the droplet. Here, the possibility of improvement in layer uniformity by the reduction of the CRE is demonstrated. Mathematical simulation of the evaporation process of the QD colloidal solution droplet is conducted by solving partial differential equations (PDEs) numerically. The Navier-Stokes equation, continuity condition, and mathematical expressions of physical parameters including the evaporative flux are used for setting up the PDEs, which are then solved with the finite difference method. A filter is included in the process to suppress unwanted instability. Using this simulation, the whole evaporation process is analyzed by observing time evolution of parameters. As a result, various conditions for reducing the CRE are found: sufficient initial concentration, proper solvent type, small contact angle, and fast evaporation rate. The outcome appears to agree with experimental data. Published under license by AIP Publishing.