Abstract
The International Telecommunication Union announced a new color gamut standard of broadcast service television (BT 2020) for ultra-high-definition TV in 2012. To satisfy the wide-color gamut standard of BT 2020, monochromatic red (R), green (G), and blue (B) emissions require a small full width at half-maximum, which is an important property for improving color purity. Although organic light-emitting diode (OLED) displays are currently one of the main types of display technologies, their broad emission via strong vibronic coupling between ground and excited states is a major hurdle to overcome in the development of next-generation wide-color gamut displays. Thus, the development of OLED emitters with narrowband R–G–B emissions is of great significance. In this review, the recent progress in the development of OLED materials with narrowband emission is summarized by grouping them into fluorescent, phosphorescent, and thermally activated delayed fluorescent emitters to reveal the correlation between molecular structures, optical properties, and device characteristics. We discuss rational molecular design strategies to achieve narrow photoluminescence and electroluminescence and the underlying mechanisms for controlling the emission bandwidth. Finally, the challenges in the realization of wide-color gamut OLED displays and the future prospects of such devices are discussed.
Highlights
Since the first organic light-emitting diode (OLED) was successfully demonstrated by Tang and Slyke in 19871, OLEDs have been extensively studied in both academia and industry, becoming a mainstream display technology in fullcolor televisions and smartphones
We focus on the molecular design of narrowband emitting fluorophores and structure-optical property correlations by categorizing the molecules into (i) twisted structures with bulky substituents with suppressed intermolecular aggregation, (ii) rigid/fused aromatic molecules without charge transfer (CT) character, (iii) 5,12-dihydroquinolino[2,3-b]acridine-7,14-dione and
To achieve both high-performance and narrowband emission in TADF OLEDs, Hatakeyama et al designed new TADF materials in which a rigid molecular framework with regular arrangements of boron and nitrogen atoms shows an Multiple resonance (MR) effect; the highest occupied molecular orbital (HOMO) is localized on the nitrogen atoms and at the meta-position with respect to the boron atom, whereas the lowest unoccupied molecular orbital (LUMO) is localized on the boron atom and at the ortho- and para-positions (Fig. 12c
Summary
48 54 53 34* 47 43 42 NA 40 40 60 35 56 46 48 49 40* 40 40 39 37 43* 21* 22* 22* 42*. Large ΔE(ZFS) values over 50 cm−1 in quasi-octahedral structures indicate significant 3MLCT character in the emitting T1 state, showing favorable radiative emission from the triplet substates to the ground S0 state via efficient SOC. The light-emitting properties of phosphorescent metal complexes can be modulated by changing the ancillary ligand Because of their higher triplet energy, nonchromophoric ancillary ligands do not influence the emission process directly, but different ligand field strengths can alter the SOC efficiency and structural distortion. The (BTMN)2Ir(acac)-based red-emissive EL device (ITO/PEDOT:PSS/PVK:(BTMN)2Ir(acac)/TPBi/ CsF/Al) showed a significantly broadened emission at 598 nm with an FWHM in the range of 74–76 nm, reinforcing the need for additional structural modifications to narrow the EL bandwidth to achieve high color purity
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