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

Abstract

Highly efficient solution‐processable emitters are greatly desired to develop low‐cost organic light‐emitting diodes (OLEDs). The recently developed thermally activated delayed fluorescence (TADF) materials are promising candidates, but blue TADF materials compatible with the all‐solution‐process have still not been achieved. Here, a series of TADF materials, named X‐4CzCN, are developed by introducing the bulky units through an unconjugated linker, which realizes high molecular weight to enhance the solvent resistance ability without disturbing the blue TADF feature. Meanwhile, the peripheral wrapping groups efficiently inhibit the triplet–triplet and triplet–polaron quenching by isolating the energy‐transfer and charge‐transporting channels. The photophysical measurements indicate that a small variation in peripheral unit will have a noticeable effect on the luminescence efficiency. The enlarged volume of peripheral units will make the electroluminescent spectra blueshift, while enhancing the energy transfer of exciplex and blocking the energy leakage of electromer can facilitate the exciton utilization. As a result, the fully solution‐processed blue OLED achieves a CIE of (0.16, 0.27), a low turn on voltage of 2.9 eV, and a high external quantum efficiency of 20.6 %. As far as we known, this is the first report of all‐solution‐processed TADF OLEDs with blue emission, which exhibits a high efficiency even comparable to the vacuum‐deposited devices.

Molecular core–shell structure design: Facilitating delayed fluorescence in aggregates toward highly efficient solution‐processed OLEDs

“…[ 27,28 ] However, the high device efficiencies of AIDF emitters are mainly achieved by vacuum deposition method, which generally is high‐cost and unfavorable for large area preparation. [ 29 ] As a contrast, solution‐process method has the advantage of low cost and large‐area preparation, while the performance of solution‐processed device mostly is disappointing. [ 30,31 ]…”

“…[27,28] However, the high device efficiencies of AIDF emitters are mainly achieved by vacuum deposition method, which generally is high-cost and unfavorable for large area preparation. [29] As a contrast, solution-process method has the advantage of low cost and large-area preparation, while the performance of solution-processed device mostly is disappointing. [30,31] Inspired by the core-shell structure in nature, herein, we proposed and designed a molecular core-shell structure by introducing flexible-chain linked bulk fragments as a shell layer to protect the core emitter for electroluminescence device.…”

Color-tunable emission from violet-blue to pure-blue based on 5,9-disubstituted pyrene derivativesviaengineering of aryl-side groups

“…Following an increase in the concentration of Py-B2An , the proportion of the extra two new peaks increased, and the peak at 552 nm was strongest at the concentration of 100%. According to the variation of the EL spectra along with increasing concentration, and considering the relatively coplanarity characteristic of Py-B2An as well as the anthracene-side group, for the extra two peaks, we speculate that they possibly originated from its excimer emission (552 nm), 62 and electromer emission 63 or the excimer emission of anthracene (524 nm), 64 respectively.…”

Highly Efficient Quasi-2D Perovskite Light-Emitting Diodes Incorporating a TADF Dendrimer as an Exciton-Retrieving Additive

“…It has been reported that these dissociated free charges can be combined in additives and reused by transferring energy to the perovskites, which is a positive effect for the device efficiency of the quasi-2D perovskite LED. − However, most of these additives follow the traditional fluorescence mechanism, which means only 25% singlet energy can be used for exciton retrieving. Recently, our group has designed and synthesized a series of thermal-activated delayed fluorescence (TADF) dendrimers for highly efficient solution-processed OLEDs. , These TADF materials not only have good film forming ability but also can suppress the concentration-quenching effect by its self-encapsulation . Using such a type of TADF material as an additive, the retrieved excitons can be 100% useful due to the efficient reverse intersystem system crossing from triplet to singlet.…”

“…Recently, our group has designed and synthesized a series of thermal-activated delayed fluorescence (TADF) dendrimers for highly efficient solution-processed OLEDs. 35,36 These TADF materials not only have good film forming ability but also can suppress the concentrationquenching effect by its self-encapsulation. 37 Using such a type of TADF material as an additive, the retrieved excitons can be 100% useful due to the efficient reverse intersystem system crossing from triplet to singlet.…”