Michele Ricks's Posts
How OLED Technology Works
Organic light emitting diode (OLED) technology uses substances that emit red, green, blue or white light when excited with an electric current. Without any other source of illumination, OLED displays present bright, clear video and images that are easy to see at almost any angle.
OLED displays stack up several thin layers of materials - a human hair is 200 times thicker than the total organic stack! As current passes through the device, the organic materials are excited. In techno-jargon, holes and electrons from the electrodes recombine to form an excited state of the emitting molecule. In order to relax again, the excited molecule gives off light that we see through the transparent substrate. Different colors of light are achieved by doping (mixing in an additive) the organic material with compounds designed to emit the desired wavelength of light.
The OLED display in Kodak's wireless picture frame is an Active matrix (AM) OLED display. These displays are fabricated on glass sheets using a low-temperature polysilicon (LTPS) semiconductor layer to build thin-film transistors (TFTs) at each point in the display (pixel) that switch the pixel on and off. The combination of TFTs and other integrated electronics (drivers) allow pixels to stay on longer and reduce the size of the display module. The use of LTPS TFT substrates also enables high-resolution (small pixels) displays that deliver smooth, high-quality video and can be scaled to sizes needed for TVs.
The OLED display is built in a multi-step process. First, the LTPS TFTs are built on a large glass substrate, the "motherglass." This is moved into a low-pressure environment for addition of the OLED layers. Next, another piece of glass is sealed to the substrate, encapsulating the OLED layers, to protect the device from oxygen and moisture. Finally, individual displays are cut from the motherglass. Many small displays can be made on motherglass sheets that can be as large as a queen-size bed!
Comments
Posted By: Michele Ricks (10/13/2008)
Comment: Great question, Don! The organic ompounds used in OLED devices are small molecules, meaning they have a lower molecular weight than polymer compounds. Some of the early materials used by Tang & Van Slyke were found in the Kodak Chemical Library, because they were used as film dyes or eletrophotographic pigments or materials. Chemicals used for modern devices are manufactured by a variety of companies, including Kodak.
Posted By: Don Stuart (10/10/2008)
Comment: This is a great tutorial; thanks Michele. What are these organic compounds or substances? Where do they originate? Thanks. Don
Posted By: Ron Mertens (10/10/2008)
Comment: If you want to read more about OLEDs, check out our interview with Mr. Corey Hewitt and Dr. James Buntaine from Kodak OLED Systems. http://www.oled-info.com/kodak/kodak_oled_systems_information_and_interview Ron