Influence of the polarity of dopants on red organic light-emitting devices

The electroluminescent properties in red organic light-emitting diodes (OLEDs) doped with polar and non-polar red emitting molecules were studied. The emission chrominance changed from red to orange along with the increase in the bias voltage in the devices doped with polar molecules; however, the emitted colour in the devices doped with non-polar molecules was unaffected by the bias voltage and the viewing angle. The reason was assumed to be the orientation of polar molecules under the electric field, so that non polar molecule is the optimum candidate for red emitting dopants used in red OLEDs to obtain stable chrominance.