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**[http://www.sciencelab.com/msds.php?msdsId=9927329 ZnO]
**[http://www.sciencelab.com/msds.php?msdsId=9927329 ZnO]


== Purification Methods/ Testing Process ==
== Purification Methods ==


*Purification Methods
*Purification Methods

Revision as of 12:46, 16 October 2013

Sample photo caption.


3D Printing CdSe/ZnS Quantum Dots on a ZnO Wafer

For the manufacturing of quantum dot LED (QLED) displays, the quantum dots will have been created prior to 3D printing. The quantum dots will be made of the semiconductor, cadmium selenide/zinc sulfide (CdSe/ZnS), which consists of CdSe core and a ZnS shell. The ZnS shell on the quantum dot acts as a protective barrier between the core, which is responsible for optical emission, and the surrounding material [1]. Four sizes of quantum dots corresponding to four colors (red, yellow, orange, green) of emitted light will be purchased from mkNano. The smallest quantum dots will be purchased from ------ since mknano did not offer CdSe/ZnS quantum dots in the size range that will emit blue light.

The CdSe/ZnS quantum dots will be 3D printed on a crystalline ZnO wafer which will act as the electron injection layer. ZnO was chosen for its favorable band gap energy and work function [2]. The ZnO wafer substrate will be purchased from Precision Micro-Optics.

The quantum dot suspensions used in this project will use water as the solvent. Some success has been realized by Haverinen et al. [3] in inkjet printing "CdSe core and CdS/ZnS double shell" quantum dots on a "cross-linkable poly-TPD [poly(N,N′-bis(4-butylphenyl-N,N′-bis(phenyl)benzidine)]" hole injection layer using chlorobenzene as a solvent. Table 1 compares various properties of chlorobenzene and water.

Table 1[4][5][6]
Solvent Vapor Pressure Surface Tension Density Viscosity
Chlorobenzene 8.8 Torr (20°C) 33.3 dyn/cm (20°C) 1.1 g/cm3 0.0008 Pa*s (20°C)
Water 17.5 Torr (20°C) 72.8 dyn/cm (20°C) 1.0 g/cm3 0.001 Pa*s (20°C)

For an initial trial, water is a good solvent to start with because the important properties of water are close to those for chlorobenzene, which was used as a solvent by Haverinen et al. to print CdSe core and CdS/ZnS quantum dots. The biggest difference between water and chlorobenzene are the vapor pressure and surface tension. Both the surface tension and vapor pressure for water are approximately twice as much as the vapor pressure and surface tension for chlorobenzene. Despite the seemingly significant differences in these properties, they are still close enough to justify attempting a trial using water as a solvent.

3D Printing Process Steps

The focus of this project is on the viability of 3D printing the quantum dot layer (CdSe/ZnS) on the electron injection layer (ZnO wafer). The other layers (cathode, hole injection layer, anode) are beyond the scope of this project. Steps involving the other layers are for clarity only.

Note: All the quantum dot colors could not be purchased from the same manufacturer. mkNano did not offer a CdSe/ZnS quantum dot capable of emitting blue light.

Steps:

  • Acquire materials
  • Filter blue light emitting quantum dots that were purchased in toluene/aliphatic amine
    • Measure 4 mg of these quantum dots and add to 1 ml of water
  • 3D print the cathode layer to the desired size
  • 3D print the electron injection layer (ZnO crystalline wafer Precision Micro-Optics) on top of the cathode
    • The electron injection layer will be 20 mm x 20 mm
  • Load the quantum dot suspensions into cartridges compatable with a printer head similar to Dimatix DMP 2800 materials printer, which was used in the study performed by Haverinen et al.[7]
  • Print the quantum dots into a display array
  • 3D print a hole injection layer onto the quantum dot layer
  • Print the final transparent anode layer onto the hole injection layer

Dia

Dia flowchart of 3D print process

Material Safety Data Sheets

Chemicals & Compounds Used

Purification Methods

  • Purification Methods
    • The CdSe/ZnS quantum dots are purchased prior to 3D printing, thus, are tested to meet the specifications set by mkNano.
    • The ZnO wafer acting as the electron injection layer is held to the standards put in place by Precision Micro-Optics.

Ink Properties

In-Situ Applications

Applications

The application of quantum dots in LED displays is still relatively new, therefore, the initial applications may begin with larger displays. Larger displays do not require as high of a resolution, making the precision less critical. Quantum dots could be included in billboards, sports arenas, traffic management, festivals, theaters, and scoreboards [8]. Once this technology is further developed, it could be utilized in smaller scale instances, which require higher resolution. These instances could include mobile screens and watches.

Costs

Table 2

Material Unit Price Total Price
CdSe/ZnS $396.00/1 mg $1584.00
CdSe/ZnS (in toluene/aliphatic) $160.20/1 mg $640.80
ZnO wafer $1200 $1200
Total Cost $3424.80

Advantages and Disadvantages of Quantum Dots in LED Displays

  • Advantages
    • Pure color: Quantum dot LED (QLEDs) displays are advantageous in that you get a more pure color than organic LEDs (OLEDs). QLEDs have been found to have 30-40% greater luminance efficiency than OLEDs.
    • Require less energy: There is an inverse relationship between luminous power efficiency and energy required to operate, therefore, there QLEDs require less energy than OLEDs.
    • Decreased manufacturing cost: The manufacturing process of LEDs using quantum dots allows the manufacturer to use less materials. Color filters, backlight, or glass[9].
    • Increased flexibility: Quantum dots can be absorbed in aqueous and non-aqueous solvents which allow for greater flexibility [10].
  • Disadvantages
    • The color emitted by quantum dots is determined by size. Blue light emitting quantum dots are the smallest. Not only is it difficult to produce this small size, but blue quantum dots require greater emission to be able to be seen [11].

OpenSCAD Code & Design

The ZnO layer (black) is the electron injection layer, while the quantum dots are printed in three different colors. The quantum dots are printed into the shape of the pixel on the screen, and can be seen scaled up, here

//electron injection layer color ("black",1) cube ( [40,40,1],center = true);

//print of blue quantum dot pixels translate ([-5,-8.33,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([5,-8.33,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([-5,1.66,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([5,1.66,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([-5,-18.33,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([5,-18.33,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([-5,11.66,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([5,11.66,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([-15,-8.33,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([15,-8.33,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([-15,1.66,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([15,1.66,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([-15,-18.33,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([15,-18.33,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([-15,11.66,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true); translate ([15,11.66,.5]) color ("blue",1) cube ( [9.3,3,.1],center = true);

//print of green quantum dot pixels translate ([-5,-5,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([5,-5,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([-5,5,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([5,5,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([-15,-5,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([15,-5,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([-15,5,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([15,5,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([-5,-15,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([5,-15,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([-5,15,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([5,15,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([-15,-15,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([15,-15,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([-15,15,.5]) color ("green",1) cube ( [9.3,3,.1],center = true); translate ([15,15,.5]) color ("green",1) cube ( [9.3,3,.1],center = true);

//print of red quantum dot pixels translate ([-5,-1.66,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([5,-1.66,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([-5,8.33,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([5,8.33,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([-15,-1.66,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([15,-1.66,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([-15,8.33,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([15,8.33,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([-5,-11.66,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([5,-11.66,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([-5,18.33,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([5,18.33,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([-15,-11.66,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([15,-11.66,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([-15,18.33,.5]) color ("red",1) cube ( [9.3,3,.1],center = true); translate ([15,18.33,.5]) color ("red",1) cube ( [9.3,3,.1],center = true);

References

Contact details

Ajmcquar Kmwhalen Shaneamtu

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