Quantum Dot Self-Assembly Deposition in Physically Confined Microscale Space by Using an Inkjet Printing Technique

Abstract

Inkjet printing technique is susceptible to form coffer-ring patterns and inhomogeneous films owing to the evaporation and its accompanying hydrodynamics of microscale quantum dot droplet. Pioneer efforts are usually confined to two-dimensional flat substrates and inks with mixed solvents/additives. Herein we demonstrate that physically confined space offers an additional parameter in tailoring such processes of droplets and the following quantum-dot self-assembly deposition, without extra modification of quantum dots or solvent chemistry. Owing to the boundary of physically confined space, two three-phase border lines in both the bottom center (horizontal direction) and the barrier of the bank substrate (vertical direction) arise, inducing dual capillary flows and Marangoni backflows. The evaporation, fluid flow, and film-forming process in physically confined space are studied by introducing well-prepared single-solvent quantum dots inks. The systematical analysis offers valuable instructions including ink preparation, surface modification, and postprocessing evaporation technique for inkjet-printed patterning applications, especially for pixelated display, polychrome patterning, and sensor array.

Lattice Boltzmann Study of Microdroplet Evaporation Process in Pixel Pits

“…After the droplet evaporates in the pixel pit, it is easy to show uneven results, such as a coffee ring. 4 The nonuniform morphology will damage the display effect, luminous efficiency, and display life of OLED devices. 5 In order to control droplet evaporation in pixel pits and obtain uniform curing morphology, the droplet evaporation dynamics at the micron scale needs to be studied.…”

“…When the droplet size is about 100 μm, the time window for evaporation is very short. While the liquid level in the pit is lower than the pit, the mainstream side-view visual observation scheme cannot capture the evaporation process . Therefore, the simulation may be the most feasible method for investigating the evaporation process of micron-sized droplets in pits.…”

“…While the liquid level in the pit is lower than the pit, the mainstream side-view visual observation scheme cannot capture the evaporation process. 4 Therefore, the simulation may be the most feasible method for investigating the evaporation process of micron-sized droplets in pits. Eales et al analyzed solution evaporation in pits with different geometric characteristics in two dimensions by solving the Navier−Stokes equations through the finite difference method.…”

Combining printing and nanoparticle assembly: Methodology and application of nanoparticle patterning

“…The higher surface-to-volume ratio at the droplet edge causes the solvent to evaporate faster than at the droplet center, resulting in an outward flow from the center to the edge, carrying the dispersed NPs to the fixed three-phase contact line (TCL). 41 Previous studies described inks composed of binary solvent mixtures that produce different evaporation rates. Fast-evaporating solvents have the highest proportion in the center, while slow-evaporating solvents are highest in proportion at the edges, resulting in surface tension driven (Marangoni) recirculating flows.…”

Spatially Ordered Arrays of Colloidal Inorganic Metal Halide Perovskite Nanocrystals via Controlled Droplet Evaporation in a Confined Geometry

“…Similarly, a confined structure with a defined hole-array with vertical microfluidic channels produced by a standard lithographic Si wafer etching process enabled the deposition of colloidal nanoparticles in a planar configuration [24]. With the progress of the integration technique for the solution processible method, a sophisticated toolkit (i.e., ink-jet printing) was ready to apply for a small-scale deposition of nanoparticles or conductive organic molecules; this computer-controlled positioning of colloidal solution through multiple nozzles is highly promising for a variety of optoelectronic applications [25]. However, the above set of experimental approaches still required other expensive equipment or a series of processing steps.…”