High‐Power‐Efficiency White Thermally Activated Delayed Fluorescence Diodes Based on Selectively Optimized Intermolecular Interactions

Abstract

Besides low cost and environmental sustainability, high power efficiency is an essential condition for daily lighting applications, and one of main challenges for thermally activated delayed fluorescence (TADF) white organic lightemitting diodes (WOLED). Here, it is demonstrated that power efficiency can be improved through accurately modulating intermolecular interactions. An asymmetrical phosphine oxide (PO) molecule named 246DBFTPO is constructed, in which the steric hindrance and inductive effect of PO groups restrain π-π stacking but form continuous intermolecular hydrogen bond networks. The steric anisotropy of PO groups leads to the heterogeneous molecular distribution in 246DBFTPO matrix, accompanied by the homogeneous intermolecular interactions. Compared to symmetrical and semisymmetrical PO congeners, 246DBFTPO provides balanced carrier transport, efficient host-dopant and dopant-dopant energy transfer, and effective quenching suppression. Based on its electron mobility of 10 −5 cm 2 V −1 s −1 and a 90% photoluminescence quantum yield of its dually doped white TADF film, 246DBFTPO is simultaneously competent as host and electron transporting material in a trilayer single-EML full-TADF WOLED, leading to a record power efficiency of 76.7 lm W −1 .

Research progress of full electroluminescent white light-emitting diodes based on a single emissive layer

“…4 . Strategy 1 normally refers to the exciton recombination regulation between the cohost and R/G/B guests in SEL–WOLEDs 17 , 20 . A wide-bandgap material acts as the host material; in contrast, materials with narrow bandgaps that emit specific colours (e.g., R/G/B) can act as guests.…”

“…Therefore, a series of studies has focused on the development of host–guest-compatible materials and ways to simplify the device structure by reducing the number of materials in phosphorescent emitter-based SEL–WOLEDs. Many materials with bipolar characteristics have been simultaneously employed as hosts, electron-transport layers, and even hole-transport layers 17 , 40 , 47 . Xue J. Y. et al designed and synthesised a multifunctional material for high-efficiency SEL–WOLEDs through simple one-pot macrocyclization (aromatic hydrocarbon component of toluene) 47 .…”

“…5c . The results of many studies indicate that bipolar materials are conducive to more balanced charges and broader recombination regions, so that the devices have higher efficiency and better colour stability 17 , 40 , 47 . In addition to the host materials, the selection and optimisation of the guest materials is also very important in realising highly efficient and colour-stable SEL–WOLEDs.…”

“…At almost the same time as WLEDs with multilayer structures 12 , 13 , SEL–WLEDs began receiving extensive attention and are continuously developing. Some organic materials that emit blue/orange 14 – 17 or red/green/blue (R/G/B) 18 – 20 light are used to generate SEL–WLEDs. Some R/G/B QDs can also be mixed in an SEL 21 – 25 , showing potential in lighting applications, especially considering the advantage of their low-cost solution-process capability.…”

Weaving host matrices with intermolecular hydrogen bonds for high-efficiency white thermally activated delayed fluorescence

“…Consequently, doped emissive layers (EML) featuring TADF emitters dispersed in inertia host matrix were widely used in high-efficiency monochromic diodes, partially leading to rapid improvement of external quantum efficiencies (η EQE ) beyond 25%. [11][12][13][14][15][16][17][18] These advances provide for developing high-performance pure-TADF WOLEDs, [19][20][21][22][23][24][25] especially based on single-EML structure [26][27][28][29][30][31][32][33] to maximize the advantages of organic materials and devices in low cost and large-scale production.…”