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Posted: May 30, 2011
First full-color display based on quantum dots
(Nanowerk News) Moving from bulky cathode-ray televisions to slimline liquid-crystal and plasma displays not only frees up space in our homes and offices, but also has the added advantage of reducing energy consumption. The development of the first full-color display based on quantum dots could mean that a new generation of even more efficient products could be just round the corner.
Quantum dots—tiny crystals of a semiconductor—create light efficiently when an electrical current is passed through them. But the real attraction of this technology is that the dots can be deposited on both rigid surfaces, such as glass, and flexible substrates like plastic. The problem, however, is that each dot only produces one color. "Quantum dots have many advantages over other emissive materials; however the lack of color-selective quantum dot patterning by conventional methods has hindered the development of full-color quantum-dot displays," explains Byoung Lyong Choi from Samsung Electronics in Korea. Choi, working with colleagues from Seoul National University and the University of Cambridge in the UK, has now come up with a simple method for obtaining red-, green- and blue-emitting quantum dots correctly arranged onto a pixelated panel ("Full-colour quantum dot displays fabricated by transfer printing").
Choi and his colleagues used a method known as transfer printing, a technique similar to that used for hundreds of years to pattern fabrics. A single layer of 'red' quantum dots was coated onto a silicon surface. A template with the required pattern was then pressed onto the surface to collect quantum dots, and then stamped onto a glass substrate covered with an array of transistors. This process was subsequently repeated for 'blue' and 'green' quantum dots.
Choi and the team managed to deposit uniform films of quantum dots of precisely controlled thickness. This level of control was crucial in order to ensure that the electronic properties of the films were stable and dependable. Previous approaches have involved the use of solvents, which has led to deterioration of device performance. The transfer-printing method, however, is solvent-free. A 4-inch display produced using the technique (see image) is 70% more power efficient than one created using the alternative spin-coating approach. "Next we hope to develop transfer printing for various other nanomaterials as well as quantum dots," says Choi.