Precise modulation of multiple resonance emitters toward efficient electroluminescence with pure-red gamut for high-definition displays

Abstract

Multiple resonance (MR) compounds have garnered substantial attention for their prospective utility in wide color gamut displays. Nevertheless, developing red MR emitters with both high efficiency and saturated emission color remains demanding. We herein introduce a comprehensive strategy for spectral tuning in the red region by simultaneously regulating the π-conjugation and electron-donating strengths of a double boron–embedded MR skeleton while preserving narrowband characteristics. The proof-of-concept materials manifested emissions from orange-red to deep red, with bandwidths below 0.12 eV. The pure-red device based on CzIDBNO displayed superior color purity with CIE coordinates of (0.701, 0.298), approaching the Broadcast Television 2020 standard. In concert with high photoluminescence quantum yield and strong horizontal dipole orientation, CzIDBNO also achieved a maximum external quantum efficiency of 32.5% and a current efficiency of 20.2 cd A −1 , outstripping prior reported organic light-emitting diodes (OLEDs) with CIE x exceeding 0.68. These findings offer a roadmap for designing high-performance emitters with exceptional color purity for future OLED material research advancements.

The third strategy: modulating emission colors of organic light-emitting diodes with UV light during the device fabrication process

“…1–4 In addition, OLED displays can exhibit an impressively high resolution and large color gamut. 5–9 Therefore, modulation of the emission colors of OLEDs is of great importance, but to date it has generally been limited to two ways. The most common way is to use different emitters with diverse molecular structures, which can emit different colors of light; thus, a lot of chemical structure design and synthesis work need to be done.…”

“Core–Shell” Wave Function Modulation in Organic Narrowband Emitters

“…Ensuring high color purity and primary red–green–blue (RGB) emission with wide-range wavelength maximum (630, 532, and 467 nm for RGB) for each individual pixel is mandatory. Notably, a wavelength shift exceeding 163 nm (∼0.69 eV) between blue and red emissions is required. − However, achieving wide-range color tuning while preserving a narrow FWHM for MR-TADF emitters is challenging owing to the atomically separated highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) distribution in the rigid heterocyclic skeleton, resulting in weak and short-range intramolecular charge transfer (ICT). − Figure a shows three mainstream strategies to redshift the MR emission, including (i) peripheral decoration of an MR unit by substituting bulky donor/acceptor (D/A) moieties, , (ii) π-conjugation extension in an MR-unit by fusing D/A fragments, , and (iii) para -(B−π–B)/(N−π–N) modulation by merging MR units. ,− Regarding (i) and (ii), the bathochromic shift of emission is constrained by the prerequisite of small FWHMs, as the MR effect should dominate over the induced twisted-ICT. , In contrast, (iii) enables a sufficient redshift because of the substantially enhanced electron-withdrawing and -donating strength achieved by delocalizing the HOMO and LUMO wave functions in the rigid backbone. , However, the highly extended heterocyclic aromatic skeleton leads to a laborious synthesis process and considerably large molecular weight, resulting in degradation during the long deposition process (at the sublimation temperature) in display manufacturing …”