Abstract
As one of the most promising technologies for next-generation lighting and displays, white organic light-emitting diodes (WOLEDs) have received enormous worldwide interest due to their outstanding properties, including high efficiency, bright luminance, wide viewing angle, fast switching, lower power consumption, ultralight and ultrathin characteristics, and flexibility. In this invited review, the main parameters which are used to characterize the performance of WOLEDs are introduced. Subsequently, the state-of-the-art strategies to achieve high-performance WOLEDs in recent years are summarized. Specifically, the manipulation of charges and excitons distribution in the four types of WOLEDs (fluorescent WOLEDs, phosphorescent WOLEDs, thermally activated delayed fluorescent WOLEDs, and fluorescent/phosphorescent hybrid WOLEDs) are comprehensively highlighted. Moreover, doping-free WOLEDs are described. Finally, issues and ways to further enhance the performance of WOLEDs are briefly clarified.
Highlights
Since the first organic light-emitting diode (OLED) reported by Tang et al [1], OLEDs have received enormous interest due to their outstanding merits, including excellent efficiency, bright luminance, ultralight, ultrathin, wide viewing angle, fast switching, lower power consumption, and their compatibility with flexible substrates [2,3,4,5]
Over the past two decades, the power efficiency (PE) of white OLEDs (WOLEDs) has been improved from 0.83 lm W−1 to >100 lm W−1 [8,9,10,11,12], demonstrating the great potential of WOLEDs for applications in the lighting and display field
For EQE, it is expressed as [23]: ηext = ηout · r · q · γ where ηout is the outcoupling factor, r is the fraction of excitons that can potentially radiatively decay, q is the photoluminescence quantum efficiency (PLQY) of emitters, and γ is the charge balance (γ ≤ 1)
Summary
Since the first organic light-emitting diode (OLED) reported by Tang et al [1], OLEDs have received enormous interest due to their outstanding merits, including excellent efficiency, bright luminance, ultralight, ultrathin, wide viewing angle, fast switching, lower power consumption, and their compatibility with flexible substrates [2,3,4,5]. To realize next-generation solid state lighting as well as high-quality display technology, white OLEDs (WOLEDs) are urgently desired. Over the past two decades, the power efficiency (PE) of WOLEDs has been improved from 0.83 lm W−1 to >100 lm W−1 [8,9,10,11,12], demonstrating the great potential of WOLEDs for applications in the lighting and display field. Plenty of companies are pursuing WOLEDs technology, such as LG Display, Samsung, Panasonic, Konica Minolta, OLED works, OSRAM, Visionox, and so on [21]. Apart from the selection of excellent emitters, the careful manipulation of device engineering plays a significant role in high-performance WOLEDs. Through furthering our understanding of WOLEDs, a large number of strategies have been proposed to enhance device engineering far. We clarify the issues and ways to further enhance the performance of WOLEDs
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