In this paper, we demonstrate the numerical simulations of the organic light-emitting device (OLED) based on a rigorous and efficient numerical method. The input parameters of such a program include the layer thickness and complex refractive index of each layer, the locations and density of the oscillating dipoles, and the emission photoluminescence spectrum. In evaluating the device performances, the output spectrum, the intensity distribution, and the viewing-angle characteristics of an OLED are concerned. Since the numerical difficulty arising from the large thickness of the glass layer in the OLED is carefully overcome, the program can simulate the optical performances with different glass substrate thickness ranged from less than one to hundreds of μm. When the glass substrate becomes thinner, multi-peak spectrum of an OLED is observed due to the strong interference effect between the two sides of the glass substrate. When the thickness of the glass substrate is reduced to less than 1 μm, the device is identical to a top-emission OLED with a two-microcavity structure. The simulation results are consistent with the Fabry-Perot cavity equation, which can be used as a guideline for optimizing the optical characteristics of an OLED from the normal direction. We have also demonstrated the procedures to maximize the total flux from an OLED which is more important than the luminance from the normal direction for the lighting application. Since our development of numerical algorithms is based on the general electromagnetic theory, the proposed model is, in principle, applicable to an OLED consisting of any number of layers.
In this paper, we demonstrate simulation results of a top-emission organic light-emitting device (TOLED) with a passivation layer and a dielectric layer. Passivation layer is usually composed of silicon dioxide (SiO2) and/or silicon nitride (Si3N4) to protect organic layers from oxygen and moisture. Dielectric layer is a high refractive index thin film for enhancing the external quantum efficiency. The TOLED device has a microcavity structure which comprised of an opaque and high reflective anode and a thin semitransparent cathode. When varying dielectric layer thickness, the output intensity changes and the spectrum peak shifts. The peaks oscillate as a function of the dielectric thickness and the period is around hundreds of nanometers depending on the refractive index of the dielectric layer. When adding the passivation layer, which is on the order of micrometers, more than single peak are observed. With a simple model, we found that the frequency difference between two peaks corresponds to the free spectral range of the fabry-perot cavity formed by passivation layer. When a passivation layers is added on the TOLED, the microcavity effect results in the presence of multi-peaks. It limits the view angle and decreases the color purity.
In this paper, we report simulation results of a top-emission organic light-emitting device (TOLED) with a passivation layer composed of silicon dioxide (SiO2) and silicon nitride (Si3N4) to protect organic layers from oxygen and moisture. Usually, the thickness of such a layer is about several micrometers. The electrode material of the device used for simulation is silver (Ag). The anode is thick and opaque while the cathode is thin and semi-transparent. The structure is capped with three pair of SiO2 and Si3N4 as the passivation layer. When SiO2 thickness is less than 2μm, the output intensity changes and the spectrum peak shifts. The peaks oscillate as a function of the SiO2 thickness and the period is about 170nm. When the SiO2 thickness is over 2μm, more than single peak are observed. With a simple model, we found that the frequency difference between two peaks corresponds to the free spectral range of the fabry-perot cavity formed by passivation layer. When a passivation layers is added on the TOLED, the microcavity effect results in the presence of multi-peaks. It limits the view angle and decreases the color purity.
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