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Two new carbazole-based donors (D), Ph2Cz and 2Ph2Cz, derived from the benchmark N,N′-dicarbazolyl-3,5-benzene (mCP) are blended with a triazine-centered acceptor (A), PO-T2T, to examine exciplex formation. The introduction of phenyl group(s) at C1 of the carbazole of mCP causes Ph2Cz and 2Ph2Cz to exhibit high-triplet states and excellent thermal stability. The red-shifted emission and delayed fluorescence observed in the Ph2Cz:PO-T2T and 2Ph2Cz:PO-T2T blends are a signature of exciplex formation with thermally activated delayed fluorescence (TADF) characteristics. The exciplex emission wavelength can be modulated by tuning the energy level at the D : A interface. The device with the Ph2Cz : PO-T2T (1 : 1) blend as the emissive layer (EML) exhibits an electroluminescence maximum wavelength (EL λmax) of 492 nm and external quantum efficiency maximum (EQEmax) of 8.51%, while the device employing the 2Ph2Cz : PO-T2T (1 : 1) blend as the EML exhibits an EL λmax of 504 nm and EQEmax of 8.51%. To further harness the excitons formed in the exciplex-forming blends, a π–A–π-type fluorescence emitter, NZDFT, was introduced as an emissive dopant. The good spectral overlap ensures efficient Förster energy transfer (FRET) between the exciplex-forming systems and the fluorescent dopant. The orange-red device employing the EML composed of 2 wt% NZDFT doped in the 2Ph2Cz : PO-T2T (1 : 2) co-host exhibits an EL λmax of 619 nm and EQEmax of 11.30%. Our study shows that the combination of an exciplex-forming blend as a co-host and a judiciously selected fluorescent dopant is an effective strategy for developing high-efficiency OLED devices with all fluorescent materials. [ABSTRACT FROM AUTHOR]

In recent years, owing to the demand for high‐efficiency phosphorescent organic light‐emitting devices (PhOLEDs), many studies have been conducted on the development of bipolar host materials. A series of imidazolyl‐phenylcarbazole‐based host materials, i. e. im‐CzP, im‐CzPCz, im‐CzPtBu, and im‐OCzP, were synthesized to obtain high‐efficiency green and red‐emitting PhOLEDs. With im‐OCzP as the host, satisfactory peak efficiencies of 22.2 (77.0 cd A−1 and 93.1 lm W−1) and 14.1 % (9.0 cd A−1 and 10.1 lm W−1) could be obtained, respectively. To further improve the performance of the devices, an electron transport material, bis‐4,6‐(3,5‐di‐3‐pyridylphenyl)‐2‐methylpyrimidine (B3PyMPM) was selected to construct a co‐hosted system. The efficiency of im‐OCzP combined with B3PyMPM forming co‐hosts could also achieve high values of 23.0 (80.0 cd A−1 and 98.8 lm W−1) and 16.5 % (10.2 cd A−1 and 13.4 lm W−1) for green and red PhOLEDs, respectively. These results exhibited that the proposed bipolar hosts have great flexibility in adjusting the carrier balance of EML in OLEDs, demonstrating their ingenious design and high potential. [ABSTRACT FROM AUTHOR]

Electrochemistry, iridium, light-emitting electrochemical cells, ionic transition metal complexes, perovskites Front Cover: Perovskite Light-Emitting Electrochemical Cells Employing Electron Injection/Transport Layers of Ionic Transition Metal Complexes (Chem. Eur. J. 71/2021) Keywords: electrochemistry; ionic transition metal complexes; iridium; light-emitting electrochemical cells; perovskites EN electrochemistry ionic transition metal complexes iridium light-emitting electrochemical cells perovskites 17722 17722 1 12/22/21 20211220 NES 211220 B A layer of ionic transition metal complex b promotes electron injection and transport, resulting in an improved carrier balance of green CsPbBr SB 3 sb perovskite/iTMC light-emitting electrochemical cells (LECs). [Extracted from the article]