Vertical natural convection models and their effect on failure analysis in electro-thermal simulation of large-surface OLEDs

Abstract

Besides classical inorganic LEDs, intelligent light sources can be also based on organic LEDs. OLEDs function as surface light sources and manufacturing of large area light sources is feasible with OLED technologies. Despite their lower luminous efficacy their other properties make OLEDs still an attractive option especially in high end indoor applications. In natural convection environment the temperature difference in the same OLED panel can reach 20–30 °C which can result in up to 30–40% difference in current density and thus, in the luminance. This difference in temperature and current density leads to differential ageing of the organic materials. CFD simulation is the obvious way to investigate natural convection environments but integration of a CFD solver in an OLED simulator may be difficult and the solution times are high. As a possible workaround to this problem, in this paper the application of five natural convection models for vertical plates in an electro-thermal field solver based OLED simulator as thermal boundary condition are presented. Steady state and transient simulation results of a free-standing 50 × 50 mm2 active surface OLED, surrounded by still air, are compared with measurement results. A typical failure type of OLEDs is thermal runaway caused by e.g. manufacturing problems, operational damages or overcurrent. The paper presents the effect of the natural convection model on the overcurrent caused thermal runaway simulation results.