ISP - July/August 2013 - (Page 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 http://www.industrial-printing.net

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

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