Abstract
The electrohydrodynamic (EHD) jet spraying process is a good method for making quantum dot (QD) layers in light-emitting diodes (LEDs). However, controlling the morphology and large-scale fabrication of the QD layers are critical for realizing all-solution-processed QD-LEDs with high performance. Three spraying techniques were used with the EHD jet spraying technique: a big circular film method, a spiral-line method, and a straight-line method. These techniques were used to obtain QD films with good uniformity. The straight-line spray showed the most promise to obtain a uniform QD layer with large area, and QD-LEDs made with this method showed better performance with a low turn-on voltage of 3.0 V, a luminance of 7801 cd/m2, and a maximum current efficiency of 2.93 cd/A.
Highlights
Conventional vacuum deposition is used to fabricate OLEDs but is not suitable for heavy metal materials like CdSe/ZnS core/shell quantum dot (QD)
In order to apply the droplets on a QD-light-emitting diodes (LEDs) multilayer, it is necessary to obtain smooth QD thin films that can cover all surfaces of ITO glass patterns
During EHD jet spraying, micro-droplets can be generated as mist particles in cone-jet mode from a solution injected into a metallic nozzle by applying a high voltage[6,17]
Summary
Conventional vacuum deposition is used to fabricate OLEDs but is not suitable for heavy metal materials like CdSe/ZnS core/shell QDs. Spin coating has been the most popular approach to fabricate QD-LED devices, mainly due to the simplicity of the method for achieving a near-monolayer of nanoparticles. QD chemistry seems rather simple, but obtaining a sufficiently small size distribution is an enormous challenge[4]. Achieving this is costly and laborious and, is the main cost factor in QD-LED manufacturing. Due to the simplicity and versatility of EHD jet printing, it has been successfully applied to obtain particulate materials with controllable configurations, morphologies, structures, thicknesses, sizes, and shapes. Using EHD jet printing, the thickness and morphology of QD patterning can be controlled through the combination of printing parameters, such as the size of the nozzle, tip height, injection rate, voltage bias, and spraying time[12,13]
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