RGB Thermally Activated Delayed Fluorescence Emitters for Organic Light‐Emitting Diodes toward Realizing the BT.2020 Standard

Abstract

With the surging demand for ultra‐high‐resolution displays, the International Telecommunication Union (ITU) announce the next‐generation color gamut standard, named ITU‐R Recommendation BT.2020, which not only sets a seductive but challenging milestone for display technologies but also urges researchers to recognize the importance of color coordinates. Organic light‐emitting diodes (OLEDs) are an important display technology in current daily life, but they face challenges in approaching the BT.2020 standard. Thermally activated delayed fluorescence (TADF) emitters have bright prospects in OLEDs because they possess 100% theoretical exciton utilization. Thus, the development of TADF emitters emitting primary red (R), green (R), and blue (B) emission is of great significance. Here, a comprehensive overview of the latest advancements in TADF emitters that exhibit Commission Internationale de l'Éclairage (CIE) coordinates surpassing the National Television System Committee (NTSC) and approaching BT.2020 standards is presented. Rational strategies for molecular designs, as well as the resulting photophysical properties and OLED performances, are discussed to elucidate the underlying mechanisms for shifting the CIE coordinates of both donor‐acceptor and multiple resonance (MR) typed TADF emitters toward the BT.2020 standard. Finally, the challenges in realization of the wide‐color‐gamut BT.2020 standard and the prospects for this research area are provided.

Bis-tridentate Ir(III) Phosphors and Blue Hyperphosphorescence with Suppressed Efficiency Roll-Off at High Brightness

“…It is intended to relay the excitation energy of phosphorescent sensitizer via Förster resonance energy transfer (FRET) to the MR TADF terminal emitter v -DABNA to which the device possesses a schematic structure depicted in Figure a. Moreover, the hyper-OLED device exhibits the narrowband EL emission peak at 472 nm, which is consistent with the emission profile of both the ν-DABNA emitter as well as relevant hyper-OLED devices employing other phosphorescent sensitizers. − This measure was aimed at the generation of narrowband blue emission demanded by the BT 2020 standard with a color chromaticity (CIE xy ) of 0.131 and 0.046, , and a blue emission was achieved with a shortened radiative lifetime, suppressed energy loss, and higher efficiencies. ,− As can be seen in Figure c and Table , the resulting hyper-OLED device displayed similar J–V characteristics to that of the MR TADF device but with a higher maximum EQE of 23.5% in reference to that of the unsensitized MR TADF OLED device (i.e., 20.7%). Remarkably, under practical high-brightness conditions of 100 and 1000 cd/m 2 , the EQE values were recorded to be 19.7 and 16.1%, and both are significantly better than 12.4 and 5.1% of the MR TADF reference device.…”

Realizing highly efficient deep-blue organic light-emitting diodes towards Rec.2020 chromaticity by restricting the vibration of the molecular framework

“…However, such structural units are scarce, which further adds to the challenge of constructing TADF emitters with a wide bandgap. 14 …”

“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 …”