The Impact of Spectral and Spatial Exciton Distributions on Optical Emission From Thin-Film Weak-Microcavity Organic Light-Emitting Diodes

We present an analytical model for the optical emission produced by sources located in a thin-film weak-microcavity formation and study the effects of the ensemble spectral and spatial distribution on the device emission properties. However derived for a general stratified media configuration, the formulation results are highly applicable for the study of nanometric organic light-emitting devices. Rigorously developed into closed-form analytical expressions using the device's thin-film weak-microcavity characteristics, they enable clear observation of the underlying physical processes that determine the emission properties of the device, as well as the impact of the exciton ensemble spectral and spatial distributions on these properties. For the sake of simplicity and clarity, we focus on a 2-D canonical configuration excited by impulsive (line) sources. Our results show that the spectral distribution of the ensemble diminishes interference effects originated in the weak microcavity formed between the substrate/air and cathode/active layer interfaces, while the spatial distribution can only impact the slow-varying component of the emission pattern, which is the consequence of the source-image interference near the highly reflecting cathode. For a typical device, the quasi-Lambertian emission pattern reported experimentally is reproduced. It should be pointed out that the incorporation of both rigorous electromagnetic analysis and the source spectral and spatial broadening effects is addressed in our report, to the best of our knowledge, for the first time. This results in a precise model capable of repeating and interpreting experimental and simulated data.