Highly Efficient and Stable Blue Organic Light‐Emitting Diodes based on Thermally Activated Delayed Fluorophor with Donor‐Void‐Acceptor Motif

Abstract

Thermally activated delayed fluorophores (TADF) with donor–acceptor (D‐A) structures always face strong conjugation between donor and acceptor segments, rendering delocalized new molecular orbitals that go against blue emission. Developing TADF emitters with blue colors, high efficiencies, and long lifetimes simultaneously is therefore challenging. Here, a D‐void‐A structure with D and A moieties connected at the void‐position where the frontier orbital from donor and acceptor cannot be distributed, resulting in nonoverlap of the orbitals is proposed. A proof‐of‐the‐concept TADF emitter with 3,6‐diphenyl‐9 H ‐carbazole (D) connected at the 3’3‐positions of 9 H ‐xanthen‐9‐one (A), the void carbon‐atom with no distribution of the highest occupied molecular orbital (HOMO) of A‐segment, realizes more efficient and blue‐shifted emission compared with the contrast D‐A isomers. The deeper HOMO‐2 of A is found to participate into conjugation rather than HOMO, providing a wider‐energy‐gap. The corresponding blue device exhibits a y color coordinate (CIE y ) of 0.252 and a maximum external quantum efficiency of 27.5%. The stability of this compound is further evaluated as a sensitizer for a multiple resonance fluorophore, realizing a long lifetime of ≈650 h at an initial luminance of 100 cd m −2 with a CIE y of 0.195 and a narrowband emission with a full‐width‐at‐half‐maxima of 21 nm.

Effect of void-carbon on blue-shifted luminescence in TADF molecules by theoretical simulations

“…Among the other molecules, the radiation rate in 36PCX is 4.21 × 10 3 s −1 , larger than the radiation rate of 1.78 × 10 1 s −1 in 26PCX, nevertheless k RISC in 36PCX (1.34 × 10 3 s −1 ) is slightly smaller than that in 26PCX (3.81 × 10 3 s −1 ). Comparing with the experimental data of the literature in Table 1, the k r in 36PCX is 2.8 × 10 7 s −1 , greater than k r of 1.1 × 10 7 s −1 in 26PCX, whereas k RISC in 36PCX (4.3 × 10 3 s −1 ) is slightly smaller than that in 26PCX Frontiers in Chemistry frontiersin.org (8.0 × 10 3 s −1 ) (Zhang et al, 2022). The experimental and calculated results differ by several orders of magnitude, but follow similar trends, which can be attributed to the fact that the calculations are performed in the gas state and experiments are measured in the dopant films (Hu et al, 2021).…”

Highly Efficient Deep‐Blue Organic Light‐Emitting Diodes Based on Rational Molecular Design and Device Engineering

“…The optimized concentrations of ν-DABNA were 0.5-1 wt% for 20-30 wt% of TADF assistant dopants. [19,30] Therefore, we initially tested 0.5:50 wt%, 1.0:50 wt%, and 1.5:50 wt% EML (Figure S17, Supporting Information and Table 3). The 0.5:50 wt% EML showed a small shoulder emission from 4PhCz2BN in the EL spectra, indicating incomplete FRET because of the low concentration.…”

Organic Electroluminescent Materials Possessing Intra- and Intermolecular Hydrogen Bond Interactions: A Mini-Review

“…An efficient deep-blue emitter can lower the power consumption, increase the color gamut of full-color OLEDs, and create other visible emissions and white light through the energy transfer processes (Lv et al, 2021;Xu et al, 2021). However, deep-blue emitters have a naturally broad bandgap, leading to a significant charge injection barrier and unbalanced charge injection and transportation in the device (Xue et al, 2017;Zhang et al, 2020;Zhang et al, 2022). Therefore, there is an essential and significant need to develop deepblue emitters with high EL efficiency and narrow-band emission.…”