Design of Blue Thermally Activated Delayed Fluorescent Emitter with Efficient Exciton Gathering Property for High-Performance Fully Solution-Processed Hybrid White OLEDs

Abstract

The blue thermally activated delay fluorescence (TADF) emitters are highly attractive in the fields of constructing hybrid white organic light-emitting diodes (WOLEDs) due to its high efficiency and color stability. However, few blue TADF emitters can withstand sequential orthogonal solvents, making it impossible to fabricate the fully solution-processed hybrid WOLEDs. Here, two TADF materials, PCz-4CzCN and TPA-4CzCN, were designed and synthesized by equipping the emissive core with nonconjugated bulky units, which can effectively enhance the solvent resistance ability without disturbing the TADF feature. The photophysical investigation indicates that phenylcarbazole unit can efficiently block the electromer formation to enhance the energy transfer and exciton utilization of the emitter. Accordingly, the blue OLEDs of PCz-4CzCN shows higher external quantum efficiency (EQE) of 22.6%, which is the best performance recorded among the fully solution-processed blue OLEDs. Upon further doping, the yellow phosphor PO-01, the fully solution-processed TADF-phosphor (T–P) hybrid WOLEDs was successfully obtained with high performance for the first time. Thanks to the efficient exciplex formation, the turn-on voltage of the white device is only 2.8 V, and the maximum brightness and power efficiency are as high as 53 300 cd m–2 and 38.5 lm W–1, respectively, which are even higher than the previous reported T–P hybrid WOLEDs with a vacuum-deposited electron transfer layer.

The Strategies for High‐Performance Single‐Emissive‐Layer White Organic Light‐Emitting Diodes

“…The T‐P hybrid WOLEDs fabricated by solution‐processing has also attracted much attraction in recent years. [ 54,56,164,165 ] The detailed EL characteristics of the solution‐processed SEL‐WOLEDs are summarized in Table 3. In 2018, Wu and Chen reported the first solution‐processed T‐P hybrid WOLED with a quaternary SEL of 26DCzPPy:TCTA:DMAC‐TRZ:Ir(dpm)PQ 2 .…”

Efficient Exciplex‐based Green and Near‐Infrared Organic Light‐Emitting Diodes Employing a Novel Donor‐Acceptor Type Donor

“…The residue was purified by flash column chromatography with eluent of petroleum ether and CH 2 Cl 2 (10 : 1) to give a white solid (yield 77%). 1…”

“…The crude product was purified with flash column chromatography with eluent of petroleum ether and CH 2 Cl 2 (8 : 1) to give a white solid (yield 88%). 1 H NMR spectrometry were recorded on a Bruker av-300 spectrometer. High-resolution mass spectrometry (HRMS) was performed with Bruker micrOTOFÀ Q II spectrometer.…”

“…In recent years, many efforts has been made in designing novel thermally activated delayed fluorescence (TADF) emitters, because 100% internal quantum efficiency (IQE) can be realized by harvesting triplet excitons via small energy gap between singlet and triplet states (ΔE ST ) and reverse intersystem crossing (RISC). [1][2][3][4][5][6][7][8][9][10] A generally used strategy to realize efficient RISC from triplet to singlet state is the spatial separation of highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), because ΔE ST is proportional to the exchange integrals between the wave functions of the LUMO and the HOMO. [2] Another pathway to realize TADF emission is forming excited-state intermolecular charge transfer (CT) complexes between electron donor and electron acceptor (exciplex), which naturally exhibits separated HOMO and LUMO distribution and small ΔE ST , because the HOMO and LUMO of are located on the donor and the acceptor molecules, respectively.…”

“…In recent years, many efforts has been made in designing novel thermally activated delayed fluorescence (TADF) emitters, because 100% internal quantum efficiency (IQE) can be realized by harvesting triplet excitons via small energy gap between singlet and triplet states (ΔE ST ) and reverse intersystem crossing (RISC) [1–10] . A generally used strategy to realize efficient RISC from triplet to singlet state is the spatial separation of highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), because ΔE ST is proportional to the exchange integrals between the wave functions of the LUMO and the HOMO [2] .…”