Recombination distribution and color tuning of multilayer organic light-emitting diode

The recombination distribution of an organic light-emitting diode with multiple emissive layers is studied theoretically. Due to the relatively low electron mobility, the recombination concentrates in the layer next to the cathode. As the voltage increases, the recombination extends to the subsequent layers because the electric field strongly enhances the electron mobility. Assume that the layers are arranged in the order of red, green, blue, and electron blocking from the cathode, the emission color can be continuously tuned by the voltage over a wide range. Taking typical material parameters and emission spectra for the layers, we show that Commission Internationale de L'Eclairage coordinate can move from (0.5,0.5) (orange) to (0.3,0.5) (green) to (0.2,0.3) (blue) as the voltage increases from 3 to 13 V. The ratio between the electron and hole mobilities of the green layer and the electron barrier between green and blue layers is found to be crucial for the wide range of color tunability. (c) 2005 American Institute of Physics.