ISP - July/August 2013 - 12

Feature
story

Quantum dots:

The next generation of displays
Explore new technologies for display printing.

david doderer

Quantum Materials Corp.

oled

TVs are a compelling new technology, but they come at
a hefty price. Not very many people are willing to pay $10,000 for
a TV, no matter how innovative it may be. To penetrate a wider
market, costs need to come down. This will require changes in
both materials and processing. Printing may be the answer that
will enable low-cost, high-definition, large-area displays.
Printed, organic LEDs are a young technology, patented in
2006 as a method for screen printing the anode, cathode, and active material. Printing has the potential to create LEDs faster and
at lower cost than vacuum-deposition methods, but it hasn’t yet
gained traction in the marketplace. Part of the challenge is that
the luminescent materials in today’s displays are not printed easily. In most OLEDs today, the active materials are small molecules, which provide better efficiency and lifetime than polymers.
The problem is that small molecules require expensive vacuum
deposition, although efforts are underway to develop small molecules that are compatible with solution processing.
The fastest route to making printed displays a reality may be to
look beyond traditional, organic molecules and consider other luminescent materials. One of the most promising is inorganic semiconductors called quantum dots—small crystals with diameters
12 | IndustrIal + specIalt y prIntIng www.industrial-printing.net

ranging from about 2-50 nm made from Group II-VI elements.
Quantum dots can be synthesized into a variety of hybrid compositions, often consisting of a core—a binary or tertiary semiconductor material—and a shell made from a semiconductor with
a band gap larger than that of the core material. Quantum dots
exhibit unique characteristics because their small size confines
the electrons within the particle.
The energy levels of different states depend on the size of the
particle. Because of this effect, quantum dots can be tuned to
emit light at any wavelength in the visible spectrum and beyond
(Figure 1). The ability to control wavelength precisely will be a
key to the success of quantum dots in displays and lighting. The
effective band gap of the dots is inversely proportional to their
size, so producing specific colors requires careful control over
diameter.
While many manufacturers produce spherical quantum dots,
this isn’t the optimum geometry. Tetrapod quantum dots, with a
central core and four symmetrical arms (Figure 2), provide better
control over dimensions and improve luminescence. The tetrapod
shape lends itself to manipulations that can produce unique performance. In these ultra-small dimensions, the tetrapod quantum



ISP - July/August 2013

Table of Contents for the Digital Edition of ISP - July/August 2013

ISP - July/August 2013
Contents
Editorial Response
Product Focus
Business Management
Printed Electronics
Quantum Dots: The Next Generation of Displays
Maintenance for Screen-Printing Presses
Perspectives on the Future of Flexible Displays
The Joy of Specs: A Discussion About Custom Systems for Industrial Applications
Printing Methods
Ad Index
Shop Tour
ISP - July/August 2013 - Intro
ISP - July/August 2013 - ISP - July/August 2013
ISP - July/August 2013 - Cover2
ISP - July/August 2013 - Contents
ISP - July/August 2013 - Editorial Response
ISP - July/August 2013 - 3
ISP - July/August 2013 - Product Focus
ISP - July/August 2013 - 5
ISP - July/August 2013 - Business Management
ISP - July/August 2013 - 7
ISP - July/August 2013 - 8
ISP - July/August 2013 - Printed Electronics
ISP - July/August 2013 - 10
ISP - July/August 2013 - 11
ISP - July/August 2013 - Quantum Dots: The Next Generation of Displays
ISP - July/August 2013 - 13
ISP - July/August 2013 - 14
ISP - July/August 2013 - 15
ISP - July/August 2013 - Maintenance for Screen-Printing Presses
ISP - July/August 2013 - 17
ISP - July/August 2013 - 18
ISP - July/August 2013 - 19
ISP - July/August 2013 - Perspectives on the Future of Flexible Displays
ISP - July/August 2013 - 21
ISP - July/August 2013 - 22
ISP - July/August 2013 - 23
ISP - July/August 2013 - The Joy of Specs: A Discussion About Custom Systems for Industrial Applications
ISP - July/August 2013 - 25
ISP - July/August 2013 - 26
ISP - July/August 2013 - 27
ISP - July/August 2013 - Printing Methods
ISP - July/August 2013 - 29
ISP - July/August 2013 - 30
ISP - July/August 2013 - Ad Index
ISP - July/August 2013 - Shop Tour
ISP - July/August 2013 - Cover3
ISP - July/August 2013 - Cover4
https://www.nxtbookmedia.com