Highly Twisted Donor–Acceptor Boron Emitter and High Triplet Host Material for Highly Efficient Blue Thermally Activated Delayed Fluorescent Device

Abstract

New highly efficient thermally activated delayed fluorescence (TADF) dopant materials (PXB-DI and PXB-mIC) for blue organic light-emitting diodes are reported. These materials were designed by combining highly conjugated rigid ring donor moieties and a boron acceptor with a highly twisted configuration to have high TADF performance and minimized self-quenching properties. In addition, a new high triplet energy and hole transport-type host material, 5-( 5 (PPBI), is also reported. This host represents deeper blue color owing to keeping the original spectra of emitters. A fabricated blue TADF device with PXB-mIC in the PPBI host exhibited maximum external quantum efficiency (EQE) of 12.5% with a CIE of (0.15, 0.08), which is close to that of the National Television System Committee blue color. The blue TADF device performances of the PPBI host was compared with the electron transport-type 2,8-bis(diphenylphosphine oxide)dibenzofuran (DBFPO) host. The blue TADF device with PXB-DI in the DBFPO host exhibited a maximum EQE of 37.4% in the sky blue region. This study demonstrates that our molecular design concept of new emitters and host is beneficial for future high-efficiency deep-blue TADF devices.

Conformational Dependence of Triplet Energies in Rotationally Hindered N‐ and S‐Heterocyclic Dimers: New Design and Measurement Rules for High Triplet Energy OLED Host Materials

“…We expect that phosphorescence measurements in other polymer hosts or in frozen solvents, where the ‘host material’ of interest is itself dispersed in another host, can lead to similarly overestimated triplet energies of novel OLED host materials, and should be avoided. As illustrative examples, phosphorescence measurements from neat films of host materials BCPO , [67] 2CzCbPy , [68] and PPBi [69] (Figure S9) performed in our laboratories indicate significantly lower triplet energies (2.72, 2.93, and 3.01 eV, respectively) than in the original reports of these materials from frozen solution (3.01, 2.97, and 3.30 eV, respectively). The revised lower E T value for PPBi and consequent potential for host quenching of deep‐blue TADF triplets may be a contributing factor to the generally lower device EQEs achieved with this host compared to phosphine‐oxide‐based hosts [69, 70] .…”

“…As illustrative examples, phosphorescence measurements from neat films of host materials BCPO , [67] 2CzCbPy , [68] and PPBi [69] (Figure S9) performed in our laboratories indicate significantly lower triplet energies (2.72, 2.93, and 3.01 eV, respectively) than in the original reports of these materials from frozen solution (3.01, 2.97, and 3.30 eV, respectively). The revised lower E T value for PPBi and consequent potential for host quenching of deep‐blue TADF triplets may be a contributing factor to the generally lower device EQEs achieved with this host compared to phosphine‐oxide‐based hosts [69, 70] . Similar differences in measurement technique are also likely responsible for the diversity of triplet energies reported for DPEPO [60, 71, 72] …”

“…However, despite the logical implications for triplet energies and how these determine host/guest compatibility, it is not commonplace to report neat film phosphorescence of new OLED host materials. Instead, low temperature solution measurements currently dominate the literature in reports of this kind [69, 76–87] . A recent study by Forrest and Thompson [73] has demonstrated that such solution measurements do not give appropriate triplet energies for the design of OLEDs, while the results here show that phosphorescence in dilute polymer films is also not suitable in this regard.…”

Disentangling Multiple Effects on Excited‐State Intramolecular Charge Transfer among Asymmetrical Tripartite PPI‐TPA/PCz Triads

“…To date, abundant typical tricolor molecular materials have been synthesized to fabricate full‐color OLED displays, [8, 9] but some issues related to the applicability remain to be resolved, and the most significant one is the blue device [10, 11] . In recent decades, development in blue electroluminescent materials have made great progress, [12] especially in terms of both color purity and device efficiency [13] . One of the most typical and earliest organic electroluminescence phenomena was discovered in single‐crystal anthracene by Pope and co‐workers in 1963 [14] .…”

“…[10,11] In recent decades, development in blue electroluminescent materials have madeg reat progress, [12] especially in termso fb oth color purity anddevice efficiency. [13] One of the most typical and earliest organic electroluminescencep henomenaw as discovered in single-crystal anthracene by Popea nd co-workersi n1 963. [14] However,i tr eadily crystallizesr ather than form an amorphous film.…”