Abstract
Recently, thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) have attracted both academic and industrial interest due to their extraordinary characteristics, such as high efficiency, low driving voltage, bright luminance, lower power consumption and potentially long lifetime. In this invited review, the fundamental concepts of TADF have been firstly introduced. Then, main approaches to realize WOLEDs based on TADF have been summarized. More specifically, the recent development of WOLEDs based on all TADF emitters, WOLEDs based on TADF and conventional fluorescence emitters, hybrid WOLEDs based on blue TADF and phosphorescence emitters and WOLEDs based on TADF exciplex host and phosphorescence dopants is highlighted. In particular, design strategies, device structures, working mechanisms and electroluminescent processes of the representative WOLEDs based on TADF are reviewed. Finally, challenges and opportunities for further enhancement of the performance of WOLEDs based on TADF are presented.
Highlights
Luminescence is a type of cold body radiation caused by external stimuli, such as electric field, mechanical stress, photoabsorption and chemical reactions [1,2,3,4,5,6]
WOLEDs based on thermally activated delayed fluorescence (TADF) emitters can exhibit nearly 20% external quantum efficiency (EQE) [56], which is comparable to state-of-the-art phosphorescence WOLEDs [57,58,59] and fluorescence/phosphorescence hybrid WOLEDs [60,61,62,63,64,65,66]
We have highlighted the recent development of WOLEDs based on all TADF emitters, WOLEDs based on TADF and conventional fluorescence emitters, hybrid
Summary
Luminescence is a type of cold body radiation caused by external stimuli, such as electric field, mechanical stress, photoabsorption and chemical reactions [1,2,3,4,5,6]. In 1987, Tang et al reported the first organic light-emitting diode (OLED) [9] In their device, charges of both polarities were injected into the organic layers and the subsequent charge transport and recombination produced green emission originating from singlet excitons; that is, fluorescence. Due to the excellent properties (e.g., noble metal-free characteristic, high efficiency, low driving voltage, bright luminance, lower power consumption and potentially long lifetime), TADF emitters have been actively investigated to develop WOLEDs [42]. WOLEDs based on TADF emitters can exhibit nearly 20% external quantum efficiency (EQE) [56], which is comparable to state-of-the-art phosphorescence WOLEDs [57,58,59] and fluorescence/phosphorescence hybrid WOLEDs [60,61,62,63,64,65,66]. WOLEDs based on TADF have great potential to the lighting and display field.
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