19-09-2017, 10:50 AM
An organic electroluminescent diode (OLED) is a light emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compound that emits light in response to an electric current. This organic semiconductor layer is located between two electrodes; typically, at least one of these electrodes is transparent. OLEDs are used to create digital displays on devices such as television screens, computer monitors, portable systems such as mobile phones, handheld game consoles and PDAs. An important area of research is the development of white OLED devices for use in solid-state lighting applications.
There are two main families of OLED: those based on small molecules and those that use polymers. The addition of mobile ions to an OLED creates a light emitting electrochemical cell (LEC) having a slightly different mode of operation. An OLED display can be operated with a passive matrix control (PMOLED) or active matrix (AMOLED) scheme. In the PMOLED scheme, each row (and line) on the screen is controlled sequentially one by one, while the AMOLED control uses a backplane of thin-film transistors to directly access and enable or disable each individual pixel, allowing one higher resolution and larger screen sizes.
An OLED display works without backlighting; therefore, it can show deep black levels and can be thinner and lighter than a liquid crystal display (LCD). In low ambient light conditions (such as a dark room), an OLED display can achieve a higher contrast ratio than an LCD display, regardless of whether the LCD uses cold cathode fluorescent lamps or an LED backlight.
Balanced load injection and transfer is required to achieve high internal efficiency, pure luminance layer emission without the contaminated emission of charge transporting layers, and high stability. A common way of balancing the load is to optimize the thickness of the cargo transport layers, but it is difficult to control. Another way is to use the exciplex. Exciplex formed between p-type transport chains and electron carriers (n-type) to locate electron-hole pairs. Energy is then transferred to the phosphor and provides high efficiency. One example of the use of exciplex is the oxadiazole grafting and carbazole side units in the red diketopyrrolopyrrole doped copolymer backbone, showing improved external quantum efficiency and color purity in any optimized OLED.
There are two main families of OLED: those based on small molecules and those that use polymers. The addition of mobile ions to an OLED creates a light emitting electrochemical cell (LEC) having a slightly different mode of operation. An OLED display can be operated with a passive matrix control (PMOLED) or active matrix (AMOLED) scheme. In the PMOLED scheme, each row (and line) on the screen is controlled sequentially one by one, while the AMOLED control uses a backplane of thin-film transistors to directly access and enable or disable each individual pixel, allowing one higher resolution and larger screen sizes.
An OLED display works without backlighting; therefore, it can show deep black levels and can be thinner and lighter than a liquid crystal display (LCD). In low ambient light conditions (such as a dark room), an OLED display can achieve a higher contrast ratio than an LCD display, regardless of whether the LCD uses cold cathode fluorescent lamps or an LED backlight.
Balanced load injection and transfer is required to achieve high internal efficiency, pure luminance layer emission without the contaminated emission of charge transporting layers, and high stability. A common way of balancing the load is to optimize the thickness of the cargo transport layers, but it is difficult to control. Another way is to use the exciplex. Exciplex formed between p-type transport chains and electron carriers (n-type) to locate electron-hole pairs. Energy is then transferred to the phosphor and provides high efficiency. One example of the use of exciplex is the oxadiazole grafting and carbazole side units in the red diketopyrrolopyrrole doped copolymer backbone, showing improved external quantum efficiency and color purity in any optimized OLED.