Evaluation of True Power Luminous Efficiency from Experimental Luminance Values

A method for obtaining true external power luminous efficiency from experimentally obtained luminance in organic light-emitting diodes (LEDs) was demonstrated. Conventional two-layer organic LEDs with different electron-transport layer thicknesses were prepared. Spatial distributions of emission intensities were observed. The large deviation in both emission spectra and spatial emission patterns were observed when the electron-transport layer thickness was varied. The deviation of emission patterns from the standard Lambertian pattern was found to cause overestimations of power luminous efficiencies as large as 30%. A method for evaluating correction factors was proposed.