Efficient Nondoped Blue Fluorescent Organic Light‐Emitting Diodes (OLEDs) with a High External Quantum Efficiency of 9.4% @ 1000 cd m⁻² Based on Phenanthroimidazole−Anthracene Derivative

Abstract

Organic light‐emitting diodes (OLEDs) can promise flexible, light weight, energy conservation, and many other advantages for next‐generation display and lighting applications. However, achieving efficient blue electroluminescence still remains a challenge. Though both phosphorescent and thermally activated delayed fluorescence materials can realize high‐efficiency via effective triplet utilization, they need to be doped into appropriate host materials and often suffer from certain degree of efficiency roll‐off. Therefore, developing efficient blue‐emitting materials suitable for nondoped device with little efficiency roll‐off is of great significance in terms of practical applications. Herein, a phenanthroimidazole−anthracene blue‐emitting material is reported that can attain high efficiency at high luminescence in nondoped OLEDs. The maximum external quantum efficiency (EQE) of nondoped device is 9.44% which is acquired at the luminescence of 1000 cd m−2. The EQE is still as high as 8.09% even the luminescence reaches 10 000 cd m−2. The maximum luminescence is ≈57 000 cd m−2. The electroluminescence (EL) spectrum shows an emission peak of 470 nm and the Commission International de L'Eclairage (CIE) coordinates is (0.14, 0.19) at the voltage of 7 V. To the best of the knowledge, this is among the best results of nondoped blue EL devices.

Efficient Bipolar Blue AIEgens for High‐Performance Nondoped Blue OLEDs and Hybrid White OLEDs

“…The absorption spectra of TPE‐TAPBI and TriPE‐TAPBI in THF solutions are shown in Figure A. Both luminogens have similar absorption spectral profiles, with absorption maxima located at 395 nm, which are associated closely to the absorption of anthracene core . The absorption spectra of both luminogens in solid films are basically the same as those in solutions (Figure S1, Supporting Information) except for 5 nm red‐shifts in peaks.…”

“…The molecular structures and synthetic routes of the new blue luminogens TPE‐TAPBI and TriPE‐TAPBI are illustrated in Scheme . Compounds 1–4 are synthesized according to the reported methods . The target compounds are obtained by Suzuki couplings between compounds 4 and 3a (or 3b) in good yields.…”

“…Anthracene is a representative building block for blue fluorescent materials owing to its good stability, strong photoluminescence (PL), and easy chemical modification . But the rigid and planar structure makes anthracene ready to form close π–π stacking, leading to severe PL quenching by aggregation, namely aggregation‐caused quenching (ACQ), and thus decreased EL performances.…”

Ternary Acceptor–Donor–Acceptor Asymmetrical Phenanthroimidazole Molecule for Highly Efficient Near‐Ultraviolet Electroluminescence with External Quantum Efficiency (EQE) >4 %

“…Additionally,t he linear relationship between luminance and current density ( Figure S2 in the Supporting Information) and as hort lifetimeo fo nly 1.2 ns in THF ( Figure S3 in the Supporting Information), suggesting there are neither thermally activatedd elayed fluorescence (TADF) nor triplet-triplet annihilation (TTA) processes. [40][41]…”

Manipulating the Molecular Backbone to Achieve Highly Emissive Sky‐Blue AIEgens and Their Applications in Nondoped Organic Light‐Emitting Diodes

“…Then the energy levels (E HOMO /E LUMO ) for the developed AIEgens were calculated according to the following equations [26] eV ( Figure 6b). [27] In contrast, after one more TPE unit was introduced into 2,7-CzTPE, the LUMO energy levels of 2,7-CzTPE were largely decreased (−2.52 eV), which is even comparable to those widely used electron-transporting materials of 1,3,5-tris(1phenyl-1Hbenzimidazol-2-yl)benzene (TPBi, −2.8 eV, Figure 6b), thus small potential barrier and also excellent electron-injection ability can be expected in the corresponding OLED devices.…”