Highly Efficient All-Solution-Processed Fluorescent Organic Light-Emitting Diodes Based on a Novel Self-Host Thermally Activated Delayed Fluorescence Emitter

Abstract

Here, we conveniently designed and synthesized a self-host thermally activated delayed fluorescence (TADF) emitter, which can not only form a uniform thin film through wet-process, but also allow the subsequently deposition of electron transporting layer (ETL) by orthogonal solvent. By using this self-host material as emitter, the all-solution-processed multilayer TADF organic light emitting diodes (OLEDs) was successfully fabricated. The maximum current, power and external quantum efficiencies of this nondoped device are 46.3 cd A, 39.3 lm W and 15.5%, respectively, which are much higher than the values of all-solution-processed OLEDs based on tranditional fluorescence and even comparable to the TADF devices with vacuum-deposited ETL. Moreover, the device maintains the high efficiency of 42.9 cd A and 39.0 cd A at the luminance of 100 cd m for display and 1000 cd m for practical lighting. The high efficiency and small efficiency roll-off of the all-solution-processed fluorescent OLEDs can be attributed to the superiority of the newly designed self-host TADF emitter, which possesses the perfect electroluminescent property and sufficient solvent resistance at the same time.

Thermally Activated Delayed Fluorescent Polymers: Structures, Properties, and Applications in OLED Devices

“…Here, it was of advantage that Cz‐CzCN is resistant to isopropyl alcohol, the solvent for ETL. A very good EQE of 15.5% with green emission had been obtained in this case . Furthermore, two counterparts of Cz‐CzCN, Cz‐3CzCN, and Cz‐4CzCN, were designed and synthesized as hosts and guests for solution‐processed TADF OLEDs (Figure ).…”

Design Strategy for Solution‐Processable Thermally Activated Delayed Fluorescence Emitters and Their Applications in Organic Light‐Emitting Diodes

“…This self‐host dendronization strategy was also employed to the well‐developed CzCB TADF chromophore by Sun and co‐workers. For instance, a five‐armed CzCB dendrimer Cz‐CzCN with Cz periphery was constructed . The nonconjugated dendrons not only maintained the distinct TADF character from the emissive core, but also rendered the material isopropyl alcohol resistant, allowing for the subsequently depositing of ETL by orthogonal solvent via a solution process.…”

Exciplex Formation and Electromer Blocking for Highly Efficient Blue Thermally Activated Delayed Fluorescence OLEDs with All‐Solution‐Processed Organic Layers

“…In fact, the advantage of solution‐processed devices for low‐cost and large‐size OLEDs require all the organic materials to be solution‐processed . Normally, to design TADF emitters compatible with a fully solution‐based process, the multifunctional properties must be centralized into one molecule, such as 1) good film forming ability through solution‐process, 2) excellent resistivity toward orthogonal solvent, and 3) restricted exciton quenching effect in the congested nondoped film state . However, it is difficult to fulfill the tradeoff between blue TADF and solvent resistance, which require material not only enlarge π‐conjugation and molecular weight to resist the solvent erosion, but also keep the small Δ E ST and blue emission unchanged.…”

“…[9] Normally, to design TADF emittersc ompatible with af ully solution-based process, the multifunctional propertiesm ustb e centralized into one molecule, such as 1) good film forming abilityt hrough solution-process, 2) excellentr esistivity toward orthogonal solvent, and 3) restricted exciton quenching effect in the congested nondoped film state. [10] However,i ti sd ifficult to fulfill the tradeoffb etween blue TADF and solvent resist-ance, which require material not only enlarge p-conjugation and molecular weightt or esist the solvent erosion, but also keep the small DE ST and blue emission unchanged. Unfortunately,t he fully solution-processed TADF blue OLEDs have been still unable to be achieved due to the lack of such multifunctional TADF blue emitters until now.T herefore, the development of novel blue TADF emittersc ompatible with fully solution-based processes and the deep investigation of the relationship between molecular structure and devicep erformance are an urgent problemstob esolved.…”