Highly Efficient, Red Delayed Fluorescent Emitters with Exothermic Reverse Intersystem Crossing via Hot Excited Triplet States

Abstract

Three donor–acceptor–donor molecular emitters have been designed by taking triphenylamine or N-phenylcarbazole as the donor and maleimide or phenyl maleimide as the acceptor, in which the highest occupied molecular orbital interaction between two donor units is maximized via the acceptor bridge. This is envisaged to enable both strong fluorescence radiation and fast exoergic reverse intersystem crossing via the second triplet state. Detailed photophysical characterization and theoretical calculations confirm that all the compounds have large oscillator strengths and short delayed fluorescence lifetimes of ∼0.2 μs. The fabricated organic light-emitting diodes (OLEDs) give red emission above 600 nm, luminance exceeding 6000 cd m–2, and external quantum efficiencies (EQEs) of over 6%. In particular, the best device shows an emission at 645 nm and a maximum EQE of 10.4%. Moreover, the EQEs remain above 3% at 1000 cd m–2 for all the emitters. This work provides an effective method to develop organic emitters for highly efficient OLEDs with low-efficiency roll-off.

Creating Side Transport Pathways in Organic Solar Cells by Introducing Delayed Fluorescence Molecules

“…In this study, we have introduced a DF small molecule, namely, MI-2TPA, 29 substantially increased fill factors (FFs) without sacrificing the short-circuit current density (J SC ). Regarding charge carrier dynamics, TA spectroscopic results indicate a significantly lengthened excited state lifetime in the ternary blends, which could mainly come from the ISC and RISC process of MI-2TPA.…”

“…In this study, we have introduced a DF small molecule, namely, MI-2TPA, to J71:IT-M-based nonfullerene organic solar cells. The chemical structures of J71, IT-M, and MI-2TPA are shown in Figure a.…”

Realization of switching between TADF and HLCT emissions through modulation of the intramolecular charge transfer character

“…From the molecular design point of view, the screening of donor and acceptor and the matching between them should be carefully considered to build the target HLCT or TADF molecule. For the donors, without loss of generality, the commonly used donors, triphenylamine (TPA) 39,40 and phenoxazine (POZ) 41,42 which have medium and strong electron-donating abilities could be used in the construction of HLCT and TADF molecules, respectively. So the key issue is how to screen an appropriate electron acceptor to match with TPA and POZ to realize the respective HLCT and TADF emissions.…”

Nuclearity Control for Efficient Thermally Activated Delayed Fluorescence in a CuI Complex and its Halogen-Bridged Dimer

“…Thus, singlet and triplet excitons generated under electrical excitation in electroluminescent devices can be used through the singlet harvesting effect − to reach up to a 100% internal efficiency, whereas a limit of only 25% is expected in the absence of TADF or phosphorescence. Although phosphorescent emitters can achieve such an efficiency through a triplet harvesting mechanism, they often require high-cost and less abundant Ir­(III) or Pt­(II) ions in their structure. − Conversely, the most studied TADF emitters correspond to purely organic compounds ,− or low-cost metal-based inorganic complexes containing Cu I ,,− or Ag I . ,,− Hence, a deep understanding and identification of the variables controlling TADF is required to design and develop high-performance emitters for technological applications.…”