Steric Rooted Multi‐Resonant Thermally Activated Delayed Fluorescent Emitters for Pure Blue Organic Light Emitting Diodes with Ultralow Efficiency Roll‐Off

Abstract

Multi‐resonant thermally activated delayed fluorescent (MR‐TADF) materials are blooming for high‐resolution organic light‐emitting diodes (OLEDs). However, boron/nitrogen (B/N)‐integrated MR‐TADF emitters suffer severe efficiency roll‐off from their strong inter‐molecular π–π interactions. Herein, versatile narrowband pure blue emitters (mono‐mx‐CzDABNA and tri‐mx‐CzDABNA) are demonstrated featuring a ring‐fused extended π‐skeleton: a classic steric hindrance and rigidity accessed by integrating with meta‐xylene (mx) rotors. tri‐mx‐CzDABNA shows a narrowband (FWHM, 26 nm) pure blue emission (λmax, 462 nm) with substantial hypsochromic shift (12 nm) while maintaining MR‐TADF characteristics. The key solid‐state analyses conclude that they conceivably suppress the non‐radiative energy loss, thus improving the photoluminescence quantum yield (PLQY > 90%) and rate of reverse intersystem crossing (RISC) (kRISC ≈2.85 × 105 s−1). The integration of tri meta‐xylene significantly leads to an enhanced horizontal dipole ratio (HDR) from 65% to 85%. Hyperfluorescent‐OLEDs are fabricated using designed MR‐TADF as terminal emitter, achieving a narrowband (FWHM, 34 nm) pure blue electroluminescence (λmax, 472 nm) and maximum external quantum efficiency (EQEmax) of 26.97% with magnificently suppressed efficiency roll‐off (7.8%) at 1000 cd m−2. So, it is believed that regulation of internal efficiencies and high color purity can amplify the route to achieving a narrowband pure blue emission through new synthetic MR‐TADF approaches.

High-performance blue OLED using multiresonance thermally activated delayed fluorescence host materials containing silicon atoms

“…The stable surface morphology of the deposited films maintains the device efficiency. Additionally, the long intermolecular distances in host materials containing the bulky TPS group may prevent triplet-triplet annihilation (TTA) and/or singlet-triplet annihilation (STA), leading to increased EQE 29 .…”

A review of fused-ring carbazole derivatives as emitter and/or host materials in organic light emitting diode (OLED) applications

“…Devices gave pure blue emission with l EL max 472 nm; CIE(0.13, 0.19), FWHM 34 nm and reduced efficiency roll-off with EQE max 26.9%; EQE 24.8% at 100 cd m À2 . 165 It is well established that MR emitters as TADF molecules can achieve high efficiency OLEDs with narrow-band emission. However, device durability can be limited because of the instability of triplet states due to the rather slow k RISC and long triplet lifetimes.…”

“…Devices gave pure blue emission with λ EL max 472 nm; CIE(0.13, 0.19), FWHM 34 nm and reduced efficiency roll-off with EQE max 26.9%; EQE 24.8% at 100 cd m −2 . 165…”

Recent Progress of Thermally Activated Delayed Fluorescent Materials with Narrowband Red, Green, and Blue (RGB) Emission

“…Then Suh. et al reported two blue emitters mono - mx -CzDABNA and tri - mx -CzDABNA featuring the steric hindrance and rigidity accessed by the integration of ring-fused extended π-skeleton and meta -xylene rotors . Both the emitters showed blue emissions at 474 (fwhm = 34 nm) and 462 nm (fwhm = 26 nm) in toluene, and the corresponding devices exhibited emissions peaked at 481 (fwhm = 48 nm) and 472 nm (fwhm = 34 nm), and showed the maximum EQEs of 21.4 and 26.9%, respectively.…”