Threshold estimation of an organic laser diode using a rate-equation model validated experimentally with a microcavity OLED submitted to nanosecond electrical pulses

Abstract

We propose a new model for the organic laser diode based on rate equations for polarons, singlet and triplet excitons for both host and guest molecules, and photon densities. The proposed model is validated experimentally by comparing calculated and measured optical responses in the context of pulsed nanosecond electrical excitation of high-speed μ-OLEDs in the limit of weak micro-cavity effects. We predict the laser threshold current density as a function of the micro-cavity quality factor, for two material gain and residual absorption values. We elucidate the crucial role played by the latter in setting the laser threshold and comment on the recently observed threshold value of ∼500 A/cm2 by the group of Adachi [1]. Simulations predict that laser action under short electrical nanosecond pulse single-shot excitation is accompanied by damped relaxation oscillations in the GHz regime. The measured ultra-short experimental optical responses at 45 V are best reproduced numerically when the Langevin recombination rate is larger than usually observed in the literature as a consequence of the field dependence of the Poole-Frenkel law for the mobility.