This work seeks to establish a quantitative method which can estimate the holes and electrons ratio in the emission zones. We fabricated multilayered white organic light-emitting diodes (WOLEDs) with the device structure of ITO/NPB(80 nm)/MADN:BUBD-1(7%)(20 nm)/MADN:DCJTB(0.3%)(20 nm)/TPBi(X nm)/LiF(2 nm)/Al as a case study on the charge recombination distribution in the emissive layer. The result shows a trend in the charge recombination ratio depending on the electron transport layer thickness. We obtained an empirical relationship between electron transport layer thicknesses and emission ratio in EML. In addition, the electroluminescent spectra were analyzed by fitting a Gaussian distribution for the two emissive layers to calculate the intensity ratio of the energy transitions. The arrival time of hole and electrons from each electrode was determined using the thickness and mobility of TPBi as electron transport layer. From these initial results, we derived an empirical mechanism to meet with a linear relationship that can allow us to design custom-made WOLEDs.
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