Viability of 3D Printing LED TV screens

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 to show why water was chosen as a solvent.

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)

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 small enough quantum dot to emit blue light.

Steps:

• Acquire materials
  • CdSe/ZnS quantum dots - red, yellow, orange, and green mkNano.
  • CdSe/ZnS quantum dots - blue Sigma Aldrich.
  • ZnO wafer (electron injection layer) Precision Micro-Optics
• 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
• Package the 5 quantum dot colors onto a vehicle (much like an inkjet printer)
• 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

Material Safety Data Sheets

Chemicals & Compounds Used

• Quantum Dots
  • CdSe/ZnS quantum dots (in water)
• Solvent
  • Water
• Substrate (Electron Injection Layer)
  • ZnO

Purification Methods/ Testing Process

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 ^[7]. 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.

• Possible Quantum Dot LED Display Applications
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Costs

Table 2

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

The pricing of the ZnO wafer is pending from Precision Micro-Optics.

References

Contact details

Ajmcquar Kmwhalen Shaneamtu

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