Non-doped red emission: A solution for bias-independent red emission

The bias dependence of the emission color of organic light-emitting devices (OLEDs) was investigated. We fabricated four red emission devices with different structures. The general bias-dependent color shift of the emissions was characterized for the first three devices. The color shift can be explained by the presence of either two different recombination zones, or a doped layer composed of two emitting materials. By avoiding the structures that induce the color shift, a bias-independent red emitting device was fabricated.