Determination of emitting dipole orientation in organic light emitting diodes

Author:

Jiang, Nan  Yang, Han-Nan  Man, Jia-Xiu  Zhang, Tao  He, Shou-Jie  Wang, Deng-Ke  Lu, Zheng-Hong  

Journal:

ORGANIC ELECTRONICS

Issue Date:

2020

Abstract(summary):

The dipole orientation of a light-emitting molecule dictates the external quantum efficiency (EQE) of an organic light emitting diode (OLED). In this paper, we studied both experimental and theoretical relationships between dipole orientation and measurable optical properties of working OLEDs. Theoretical electroluminescence (EL) spectrum, EQE, and luminance angle distribution are simulated by incorporating the dipole radiation pattern into Fabry- Perot cavity theory with horizontal dipole ratio as a variable parameter. The horizontal ratio is determined by optimizing the fitness of theoretical EL spectra to the experimental data and EL angular distribution. We show that the optical model proposed in this paper describes well the emission dipole dependent device optical data including EL spectra, EQEs, and EL luminance angular distributions. The emission fill factor (EFF), defined as the area ratio of EL angular distribution to the Lambertian curve, is found to follow a linear relationship with horizontal dipole ratio. These results provide a simple guide to deduce dipole orientations in working OLEDs.