Contents I. Introduction
In general, it is accepted that the external quantum efficiency of the organic polymer light-emitting devices (PLEDs) is limited by several major losses: charge injection at the contacts (anode and cathode), charge transport within the organic materials, electron and hole radiative recombination, photoluminescent efficiency, and light out-coupling efficiency [3]. Using a standard refraction theory, it was estimated that the photon out-coupling efficiency is about 1/5 of the total internally generated photons [2]. Several methods for improving the light out-coupling efficiency have been used to overcome this limitation set by the light escape cone of the substrate. These methods include introduction of textured surfaces or interfaces [4], [5], usage of ordered microlens arrays or microsphere media [6], [7], usage of reflecting surfaces or distributed Bragg reflectors [8], [9], and usage of a thin silica aerogel layer [10]. Several models have also been proposed for modeling optical transport in organic light-emitting devices, such as the half-space optical model [11], one-dimensional ray-tracing [5], and quantum mechanical microcavity model [12], [13], [26]. We have used a Monte Carlo approach to analyze the PLED light out-coupling efficiency [1]. This method has the flexibility for modeling events such as absorption, wave-guiding, scattering, out-coupling, and trapping in the light-emitting devices. The advantage of the Monte Carlo simulation method is that it takes into account the details of device geometry. The Monte Carlo simulation includes the angular and spectral distributions of the emitted photons, the point-spread function, the specular and diffuse reflection coefficients, and a summary of scattering events statistics.
