switched to control the light valves that form the image. As these transistors are based on silicon, the glass substrate material is chosen to match the coefficient of thermal expansion of silicon, which is relatively low. Cover glass, by contrast, has relatively high thermal expansion, as this is currently thought necessary to achieve a glass capable of ion exchange. Nevertheless, if an internal polarizer were to be achieved, researchers would be highly motivated to create a glass that combines cover and color filter functionality.
In order to form a light-emitting device, the light-emitting organic layer of an organic light-emitting diode (OLED) requires several other layers. These include a transparent substrate, which can be either rigid or flexible, depending on the application; a transparent conducting anode; a conducting organic layer; the organic light-emitting layer; and a cathode, which may or may not be transparent, depending on the application.
In operation, an electrical potential is applied across the OLED by connecting a battery or other power source between the cathode and the anode, causing a current to flow. The current flow results in electrons being removed from the molecules in the emissive organic layer, creating holes. When these holes are filled at the interface with the conducting organic layer, the electrons give up their excess energy as photons. The intensity of the emitted light is determined by the total current flow, and the color is determined by the energy level of the hole that is filled by the electrons. This, in turn, is determined by the properties of the organic molecules, allowing OLEDs to be used in color displays.
OLEDs can be made on transparent substrates to form an all-transparent display, or on an opaque or reflective substrate. In the former case, it makes possible what is known as a heads-up display, since only the displayed information interrupts the visual field.
“Flexible display technology” is a term used for a desirable technology for the next generation of cell phones, military devices, and reading devices. A device with flexible display technology would enable the user to overcome the fear of breaking, bending, or scratching the device.
One type of flexible display technology uses organic films constructed from OLEDs, which in turn are made from layers of organic material and the conductive materials needed to inject electrons and holes. When a voltage of proper polarity is applied to the conductive layers, electrons from one layer combine with the holes