In short, OLED technology delivers an incredible picture on a thin screen because no backlight is needed.
OLED technology is intended foremost as picture elements in everyday display devices. Originally developed by Kodak in the late 1970s and since refined by a many companies, OLEDs are the future alternative to LCDs (liquid crystal displays). In addition to soaking up less electricity than LCDs, OLEDs are easier to manufacture, cheaper to build, and brighter to view. Another huge benefit of OLEDs is that they do not require a backlight to function, therefore needing far less power, and when operated by a battery can last much longer.
OLEDs can also be quite thin, leading visionaries to imagine stock quotes scrolling across your pen.