Improving the Brightness and Daylight Contrast of Organic Light‐Emitting Diodes

Abstract

Abstract For most applications of displays based on organic light‐emitting diodes (LEDs), it is desirable to have good daylight contrast in combination with a high intensity of emitted light. The conventional approaches to enhance the daylight contrast, using a black cathode or circular polarizers, result in a significant loss of light emitted by the LED. A rather novel approach to enhance daylight contrast while keeping loss of emitted light to a minimum is the introduction of a chiral‐nematic film in the device. This approach leads to an increase in light efficiency by a factor of 1.8 (with respect to circular polarizers) with some loss in daylight contrast values within the reflection band of the chiral‐nematic film. Outside the reflection band, however, the contrast approaches infinity.