Modeling the Charge and Exciton Distributions in Phosphorescent White Organic Light-Emitting Diodes

Abstract

A comprehensive numerical model is developed to quantitatively analyze the charge and exciton distributions in phosphorescent white organic lightemitting diodes (WOLEDs). The model encompasses bipolar charge driftdiffusion transport with doping-dependent charge mobilities, field-dependent charge hopping across multiple interfaces, exciton generation, diffusion, energy transfer, radiative decay, and non-radiative exciton annihilation. The model is validated by direct measurement of the exciton distribution in monochromatic phosphorescent OLEDs. It is then applied to complex, multilayer WOLEDs, where it is used to accurately predict their intensity and current-dependent spectral shifts. The magnitudes of different exciton loss channels in WOLEDs are calculated and quantitatively compared. This model provides an alternative to the many experimental iterations commonly used to optimize the color balance of complex OLEDs. In this context, the model inspired the addition of a hole-blocking layer in the WOLED to balance the charge conduction and reduce spectral shifts�a design that is verified by the experiment.

Advances in Host-Free White Organic Light-Emitting Diodes Utilizing Thermally Activated Delayed Fluorescence: A Comprehensive Review

“…The trap effect in the device arises from the host and adjacent layers having a significant energy gap [ 103 ], resulting in a large energy barrier for charge injection into the host layer. Additionally, the emitter possesses a deeper Lowest Unoccupied Molecular Orbital (LUMO) level and a shallower Highest Occupied Molecular Orbital (HUMO) level compared to the host, enabling direct charge injection and subsequent radiative decay in the emissive layer [ 104 , 105 ]. Notably, the HOMO level of BDMAc, an emitter in the optimized device, closely aligns with both the two emitters and the HOMO level of PEDOT: PSS, minimizing the energy barrier.…”

Solution-processed dendrimer-based bis-tridentate iridium(iii) complexes with red, green, and blue phosphorescence for white OLEDs

“…Organic LEDs (OLEDs) are surface emitters and potential candidates for low-embedded energy, efficient solid-state lighting. White OLEDs (WOLEDs) have been achieved using fluorescent, 3 phosphorescent 4 and thermally activated delayed fluorescence (TADF) 5 emitters as well as combinations of the different types of materials. 6 While evaporative deposition techniques can be used to fabricate pixelated WOLEDs of different architectures in which red, green and blue light are generated in separate layers of a pixel or separate pixels, 7 there would be an advantage to having a single emissive layer 8 capable of emitting white light that could be processed using solution coating techniques with low-embedded energy.…”