Improving the Power Efficiency of Solution‐Processed Phosphorescent WOLEDs with a Self‐Host Blue Iridium Dendrimer

Abstract

Solution‐processed phosphorescent white organic light‐emitting diodes (WOLEDs) with improved power efficiency are reported by simply blending a yellow phosphor Ir(Flpy‐CF3)3 into a self‐host blue Ir dendrimer B‐G2. Attributable to the elimination of the host‐induced power efficiency losses existed in the traditional host‐based devices, a state‐of‐the‐art total power efficiency as high as 48.8–62.8 lm W−1 is achieved at a practical luminance of 1000 cd m−2. Moreover, without considerably sacrificing the power efficiency, the related correlated color temperature and Commission Internationale de L'Eclairage coordinates can be well tuned to satisfy different illumination requirements. The results clearly demonstrate that the adoption of a self‐host blue phosphorescent dendrimer instead of the traditional host‐based device structure is a superior and promising strategy to realize power‐efficient white‐light emitting devices.

High-Efficiency Solution-Processed Organic Light-Emitting Diodes with Tetradentate Platinum(II) Emitters

“…Owing to easy fabrication, lightweight, and capability of building on flexible substrates, this kind of device has potential application in flexible and low-cost displays, such as electronic paper and bendable displays that can be integrated into curved surfaces. However, the performance of early solution-processed OLEDs was limited by the fluorescence nature of conjugated organic polymers, − as only singlet excitons can emit light while triplet ones are wasted due to inefficient spin–orbit coupling. , In this regard, thermally activated delayed fluorescent (TADF) emitters and phosphorescent metal complexes have been extensively studied and used to fabricate solution-processed OLEDs, as both singlet and triplet excitons can be utilized. − Among the various phosphorescent emitters reported in the literature, only Ir­(III) complexes have been intensively studied as the emitting dopant in solution-processed OLEDs . These complexes have been physically or chemically dispersed in conjugated polymers or small molecular hosts to construct the emitting layer (EML) of the solution-processed OLEDs. − ,− High external quantum efficiencies (EQEs) of up to 28.5, 29, and 28.5% have been achieved in red, green, and white single-cell light-emitting devices, respectively. , Kido and co-workers reported a high EQE of 28% at a high luminance of 5000 cd m –2 in tandem solution-processed OLEDs .…”

“…However, the performance of early solution-processed OLEDs was limited by the fluorescence nature of conjugated organic polymers, − as only singlet excitons can emit light while triplet ones are wasted due to inefficient spin–orbit coupling. , In this regard, thermally activated delayed fluorescent (TADF) emitters and phosphorescent metal complexes have been extensively studied and used to fabricate solution-processed OLEDs, as both singlet and triplet excitons can be utilized. − Among the various phosphorescent emitters reported in the literature, only Ir­(III) complexes have been intensively studied as the emitting dopant in solution-processed OLEDs . These complexes have been physically or chemically dispersed in conjugated polymers or small molecular hosts to construct the emitting layer (EML) of the solution-processed OLEDs. − ,− High external quantum efficiencies (EQEs) of up to 28.5, 29, and 28.5% have been achieved in red, green, and white single-cell light-emitting devices, respectively. , Kido and co-workers reported a high EQE of 28% at a high luminance of 5000 cd m –2 in tandem solution-processed OLEDs . Nonetheless, research on the use of other efficient metal phosphors, such as platinum­(II) complexes, − as an emitting dopant in solution-processed OLEDs is in its infancy. ,− As Pt­(II) emitters usually adopt a planar molecular structure, it is envisioned that the horizontal dipole ratio could be higher, which is beneficial to achieving higher out-coupling efficiency.…”

Strategy for the Realization of Highly Efficient Solution-Processed All-Fluorescence White OLEDs—Encapsulated Thermally Activated Delayed Fluorescent Yellow Emitters

“…White organic light-emitting diodes (WOLEDs) have been extensively studied due to their great promise for universal application in future solid-state lighting sources. − To harvest 100% electrogenerated excitons for emission, organometallic emitters with a strong spin–orbit coupling effect have been widely used in all-phosphorescence WOLEDs or fluorescence/phosphorescence hybrid WOLEDs. − However, these precious-metal complexes are expensive and rare, which would limit the cost effectiveness and long-term mass production of WOLEDs. In addition to material selection, the fabricating technique is the other main source of cost.…”

Unravelling Electroplex Emission from Long-Range Charge Transfer Based on a Phosphorescent Dendrimer as the Electron Donor

“…In the past two decades, the replacement of fluorescent materials by phosphorescent ones has attracted extensive attention in both academia and industry owing to the theoretical 100% exciton-harvesting ability. − In particular, compared with the commercialized and expensive vacuum-deposition emitters, − solution-processed compounds exhibit the fascinating characteristics of low cost and large-area processes. − Among three classes of solution-processable emitters, that is, small molecules, − dendrimers, − and polymers, , the dendrimers integrate the merits of both the well-defined structure of small molecules and the good solution processability of polymers. More importantly, the peripheral dendron wrapping around the central core not only can effectively prevent the quenching/aggregation of the emissive cores but also can maintain the intrinsic emissive characteristics.…”

“…More importantly, the peripheral dendron wrapping around the central core not only can effectively prevent the quenching/aggregation of the emissive cores but also can maintain the intrinsic emissive characteristics. It is well known that the carbazole-based substituent is a typical hole-transporting group that has been proverbially introduced as the host shell in the dendrimer emitters. − ,− Recently, Lee’s group verified another promising application of the electroplex. They utilized common carbazole-based hole-transporting materials, for example, 4,4′-di­(9 H -carbazol-9-yl)-1,1′-biphenyl (CBP) and 3,3-di­(9 H -carbazol-9-yl)­biphenyl (mCBP), to integrate with the electron-transporting materials and thus form the electroplex host for red, yellow, green, and blue phosphorescent OLEDs. , Our group has proven that the dendrimer based on the carbazole dendrons has the ability to form an interfacial exciplex with the ETL. , These studies predict that the dendrimer emitters with the carbazole dendrons have a potential possibility of forming an electroplex, which is fairly stable under the electrical field excitation.…”