OLED is composed of a thin and transparent semiconductor indium tin oxide (ITO), connected to the positive electrode of electricity, plus another metal cathode, wrapped into a sandwich-like structure. The whole structure layer includes: hole transport layer (HTL), light emitting layer (EL) and electron transport layer (ETL). When the power supply to the appropriate voltage, the positive hole and the cathode charge will be combined in the luminescent layer, producing light, according to the formula of different red, green and blue RGB three primary colors, constitute the basic color. The characteristics of OLED is its own light, unlike TFT LCD need backlight, so the visibility and brightness are high, followed by low voltage demand and high power saving efficiency, coupled with fast reaction, light weight, thin thickness, simple structure, low cost, is regarded as one of the most promising products in the 21st century.
There are two driving methods for OLED, namely active drive and passive drive.