Influences of wide-angle and multi-beam interference on the chromaticity and efficiency of top-emitting white organic light-emitting diodes

Abstract

Wide-angle interference (WI) and multi-beam interference (MI) in microcavity are analyzed separately to improve chromaticity and efficiency of the top-emitting white organic light-emitting diodes (TWOLEDs). A classic electromagnetic theory is used to calculate the resonance intensities of WI and MI in top-emitting organic light-emitting diodes (TOLEDs) with influence factors (e.g., electrodes and exciton locations) being considered. The role of WI on the performances of TOLEDs is revealed through using δ-doping technology and comparing blue and red EML positions in top-emitting and bottom-emitting devices. The blue light intensity significantly increases and the chromaticity of TWOLEDs is further improved with the use of enhanced WI (the blue emitting layer moving towards the reflective electrode) in the case of a weak MI. In addition, the effect of the thicknesses of light output layer and carrier transport layers on WI and MI are also investigated. Apart from the microcavity effect, other factors, e.g., carrier balance and carrier recombination regions are considered to obtain TWOLEDs with high efficiency and improved chromaticity near white light equal-energy point.

Top-Emitting Active-Matrix Quantum Dot Light-Emitting Diode Array with Optical Microcavity for Micro QLED Display

“…Figure 5 a schematically shows the two interference modes occurring in BEQLED and TEQLED, i.e., wide-angle and multi-beam interference. The constructive interference conditions are given below [ 56 ]. where n and d are the refractive index and the thickness of the layer, respectively.…”

Top‐Emitting Quantum Dot Light‐Emitting Diodes: Theory, Optimization, and Application

“…Thus, this weak multi-beam interference, which is known to be a major contributor to microcavity enhancement, leads to a subtle microcavity effect in BQLEDs. [42] Meanwhile, for TQLEDs, both interferences are evident as the active layers are sandwiched between two coplanar reflectors. Comprehensively, optimized microcavity resonance in TQLEDs can be achieved by appropriately adjusting the thickness and the refractive index (n) of each layer, which can improve the color purity and light extraction.…”

Solution-processed, top-emitting, microcavity polymer light-emitting diodes for the pure red, green, blue and near white emission

“…Fortunately, the utilization of Fabry-Perot microcavity on OLEDs is able to narrow down the emission spectra effectively [7,8]. To date, high efficiency microcavity OLEDs are achieved from small molecular light-emitting materials by using full vapor deposition technology, in which more than ten functional layers are needed to meet all requirements of the electrics and optics [9][10][11][12]. On the other hand, luminescent polymers possess unique advantages on solution-processing, as well as high flexibility in chemical modification and color regulation.…”