INTRODUCTION

As thin display technology improves, TV sets will be available in wider shapes and sizes. Fold-up TVs and wearable TVs, similar to wearable PCs will be launched soon.

A plethora of display technologies catering to different requirements of different applications are available. Electroluminescent(EL) displays, vacuum fluorescent displays (VFDs), and light emitting diodes (LEDs) have a wide operating temperature range and luminescent characteristics

OLEDs are lightweight, durable, power efficient and ideal for portable applications. OLEDs have fewer process steps and also use both fewer and lower- cost materials than LCD displays. Universal Display believes that OLEDs can replace the current technology in many applications due to the following performance advantages over LCD.

¢ Greater brightness
¢ Faster response time for full motion video
¢ Fuller viewing angles
¢ Lighter weight
¢ Greater environmental durability
¢ More power efficiency
¢ Broader operating temperature ranges
¢ Greater cost-effectiveness




Displays are an essential element of industrial and Consumer products. Once considered as simple indicator lights, these have become vital in the performance of computing, medical imaging, process control and entertainment systems. From video systems to kitchen appliances and portable computers, or even your digital watch, displays are inevitable.

Most devices provide users with useful information on a display. In a way, the display is an indicator of the quality of that product. If the information depicted is consistently wrong-for instance, a watch always running fast”the quality of the product is perceived as poor. The same is true with information display. The poor quality of the image displayed means that the product is also of poor quality.

A plethora of display technologies catering to different requirements of different applications are available. Electroluminescent (EL) displays, vacuum fluorescent displays (VFDs), and light-emitting diodes (LEDs) have a wide operating temperature range and luminance characteristics, but limited colour reproduction. EL displays are suited to instrumentation and military applications, while VFDs are used in automotive dashboards and traffic lights. Organic LEDs (OLEDs) are likely to replace liquid crystal displays (LCDs) in the near future.

Digital display technology (DDT) is a breakthrough in visual technology. It enables engineers to create thin wide-screen TVs, flat TVs, wall TVs, and even TV screens that you can fold up like newspapers. Professor Ifor Samuel at the University of St Andrews in Scotland, who is conducting research on this technology, predicts, In a few years, it will be possible to make TV screens which can he rolled up when not in use, information displays on roller blinds, and light-emitting clothing for fashion or safety applications. So days are not far off when you will be able to customise the shape of your TV as if it were an article of clothing.

EVOLUTION

Organic semiconductors have been the subjects of intense scientific investigation for the past 50 years. These materials primarily consist of carbon, hydrogen and oxygen. Organic materialsâ„¢ weak intermolecular bonds in the solid state give them properties of both semiconductors and insulators. Organic semiconductors attracted industrial interest when it was recognized that many of them are photoconductive under visible light. This discovery led to their use in electro photography and as light valves in LCDs.

Organic materials have often proved to be unstable. When exposed to air, water, or ultraviolet light, their electronic properties can degrade rapidly. Low carrier mobility characteristic of organic materials obviates their use in high- frequency (greater than 10 MHZ) applications. These shortcomings are compounded by the difficulty of both purifying and doping the materials.

But in1987 Ching Tang and Steven Van Slyke of Eastman Kodak Co., Rochester, N.Y., successfully addressed many of these problems when they produced the first efficient light emission from a two-layer organic structure resembling a pn junction. The Kodak group used a class of synthetic dyes to develop a device called a small-molecule OLED that produced light with about 1 percent efficiency. The materials used consist of often no more than 30 or 40 atoms covalently bonded into stable individual molecular units called monomers.

Unlike small molecule compounds, polymers are long chain molecules whose monomer segments are attached in a continuous covalently bonded high- molecular weight chain. Polymers tend to be environmentally rugged and flexible although, like small molecules, their electronic properties can rapidly degrade when exposed to oxygen or water.

CONSTRUCTION

A fundamental difference between small molecule and polymeric device is the manner in which they are constructed.

Small molecule OLEDs are grown on a glass or plastic substrate to form a multi-layer structure about 100 nm thick. The substrate is first coated with a conducting transparent electrode such as indium tin oxide (ITO) which serves as the anode. This is followed by a thin hole-transporting organic layer HTL. Typically made from chemicals called diamines. An organic light-emitting layer of comparable thickness is then deposited on the ETL surface. A low work function is necessary to ensure efficient low-resistance injection of electrons from the cathode on to the ETL.