Management of Singlet and Triplet Excitons in a Single Emission Layer: A Simple Approach for a High‐Efficiency Fluorescence/Phosphorescence Hybrid White Organic Light‐Emitting Device

Abstract

A high-efficiency single-emission-layer (EML) hybrid white organic light emitting device is fabricated based on an ideal sky-blue fluorophor, DADBT, using a novel doping concentration regulation strategy, which effectively separates and respectively utilizes the singlet and triplet excitons in the single-EML. The white device shows excellent electroluminescence performance with maximum total efficiencies of 26.6%, 53.5 cd A(-1) and 67.2 lm W(-1) .

Highly efficient hybrid warm white organic light-emitting diodes using a blue thermally activated delayed fluorescence emitter: exploiting the external heavy-atom effect

“…S9c-9e, the blue emission intensities of the devices are gradually increased with increasing voltage, similar to the previous reported hybrid WOLEDs. 8 with Commission International de L9Eclairage coordinates of (0.445, 0.405), exhibiting higher intensity in the orange region. 6 In addition, candle-light-style OLEDs emitting yellowish orange light have been demonstrated to be a physiologically friendly light at night.…”

“…6 Therefore, a 'triplet harvesting' strategy by doping a blue fluorophor and red/green phosphors in separated regions of high-triplet-energy host materials has been proposed 1, 10 and is further improved by incorporating blue fluorophors with high triplet energy (T 1 ) to prevent the undesirable 'back energy transfer' from the phosphors to the blue fluorophors. 2,7,8 However, the heavy metal in the phosphors introduce an external heavy-atom effect (EHA) in the emissive layer (EML) and may lead to quenching of the fluorescence due to the increased singlet (S 1 )-triplet (T 1 ) intersystem crossing (ISC) rate (k ISC ) constant and the radiative or non-radiative decay rate of triplet excitons (k p ) of the fluorophors. [11][12][13] This process could be another possible mechanism of energy loss in hybrid WOLEDs, especially for the WOLED with a single EML, even though this process has been ignored in previous studies.…”

“…5,6 Efforts have been devoted to resolve the tradeoff between the high efficiency and long lifetime by combining the advantages of phosphors and fluorophors, that is, by fabricating hybrid WOLEDs with blue fluorophors and green/red or orange phosphors. [6][7][8][9] To attain high efficiencies in hybrid WOLEDs, mutual quenching of the fluorophors and phosphors should be minimized. It has been long realized that the quenching of the green and red phosphorescence by the low triplet energy fluorophors is one of the main losses of excitation energy in these devices.…”

“…6 Therefore, a 'triplet harvesting' strategy by doping a blue fluorophor and red/green phosphors in separated regions of high-triplet-energy host materials has been proposed 1,10 and is further improved by incorporating blue fluorophors with high triplet energy (T 1 ) to prevent the undesirable 'back energy transfer' from the phosphors to the blue fluorophors. 2,7,8 However, the heavy metal in the phosphors introduce an external heavy-atom effect (EHA) in the emissive layer (EML) and may lead to …”

High-efficiency/CRI/color stability warm white organic light-emitting diodes by incorporating ultrathin phosphorescence layers in a blue fluorescence layer

“…In order to achieve high device efficiency, phosphorescent materials have been widely used to fabricate such devices because they allow manufacturers to harvest 25% singlet excitons and 75% triplet excitons, thus achieving internal quantum efficiency of 100%, compared with the 25% theoretical value for fluorescent materials [3][4][5][6][7][8]. However, the all-phosphorescent WOLEDs are limited by i) the absence of efficient blue phosphors with long operational lifetimes that are suitable for commercial applications [9,10], and ii) the difficulty of conducting carrier injection from an adjacent carrier transporting layer to the large-bandgap host material with higher triplet state energy [11]. Thus, one promising approach to achieve WOLEDs with high efficiency and long lifetime is to combine emissions from blue fluorophores and long wavelength phosphors, also called fluorescence/ phosphorescence (F/P)-based hybrid WOLEDs.…”