Abstract
Tandem white organic light-emitting diodes (WOLEDs) are promising for the lighting and displays field since their current efficiency, external quantum efficiency and lifetime can be strikingly enhanced compared with single-unit devices. In this invited review, we have firstly described fundamental concepts of tandem device architectures and their use in WOLEDs. Then, we have summarized the state-of-the-art strategies to achieve high-performance tandem WOLEDs in recent years. Specifically, we have highlighted the developments in the four types of tandem WOLEDs (i.e., tandem fluorescent WOLEDs, tandem phosphorescent WOLEDs, tandem thermally activated delayed fluorescent WOLEDs, and tandem hybrid WOLEDs). Furthermore, we have introduced doping-free tandem WOLEDs. In the end, we have given an outlook for the future development of tandem WOLEDs.
Highlights
In recent years, organic light-emitting diodes (OLEDs) have entered the mainstream display market, since they can show comparable performance with the liquid crystal displays [1,2,3,4,5]
Based on the above facts, highly efficient phosphorescent and thermally activated delayed fluorescence (TADF) emitters are usually adopted in tandem white organic light-emitting diodes (WOLEDs), which is expected to harvest both singlet and triplet excitons for the high performance [92,93,94,95,96,97]
Based on the employed emitters, tandem WOLEDs can be classified into four types, i.e., tandem fluorescent WOLEDs, tandem phosphorescent WOLEDs, tandem TADF WOLEDs, and tandem hybrid
Summary
Organic light-emitting diodes (OLEDs) have entered the mainstream display market, since they can show comparable performance with the liquid crystal displays [1,2,3,4,5]. With the evolution of emitters and enhancement of device engineering, both phosphorescent and thermally activated delayed fluorescence (TADF) materials-based OLEDs can realize a theoretical unity internal quantum efficiency (IQE) due to the harvest of totally singlet and triplet excitons [17,18,19,20]. For phosphorescent materials, they harness singlets and triplets due to the heavy-atom effect [21,22,23]. An outlook for the future development of tandem WOLEDs will be presented
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