4. Obtaining white OLEDs

In humans, color perception is governed by three families of photoreceptors in the back of the eye, sensitive to the three primary colors: green, red and blue. The electromagnetic spectrum of sunlight covers the entire visible spectrum (in a range of wavelengths from 380 to 780 nm). When we perceive sunlight, it appears white because it excites these different photoreceptors in a balanced way. As individual conjugated organic molecules have relatively broad emission spectra, it is possible to obtain white light by judiciously combining the emission of several compounds. This concept, based on the physiology of the human eye, is used to design organic light-emitting diodes that emit white light. To achieve this, researchers exploit the emission of the three primary colors or two complementary colors (blue and yellow) within various device architectures.