Donor–Acceptor Biarylcarbazoles as Efficient Host Materials for Solution-Processable High-Performance Phosphorescent Organic Light-Emitting Diodes

Abstract

Host materials having high triplet energies offer great commercial potential for the development of solution-processable high-performance phosphorescent organic light-emitting diodes (PhOLEDs). While plenty of vacuum-deposited host materials are available, the literature reveals a dearth of solution-processable host materials. Therefore, a series of biarylcarbazoles (BACs) were designed as host materials by incorporating donor–acceptor functionalities and doped with blue, green, yellow, and orange phosphorescent emitters to develop energy-saving high-performance PhOLEDs with low turn-on voltages. All of the synthesized host materials exhibited good thermal stability in the range of 294–355 °C and exhibited remarkably high triplet energies of 2.50–2.81 eV. Surprisingly, PhOLEDs prepared by incorporating a host material 6a doped with a green phosphorescent emitter, i.e., Ir(ppy)3, displayed admirable efficiencies with a maximum power efficiency (PE) of 55.6 lm/W, a current efficiency (CE) of 53.2 cd/A, and an external quantum efficiency of 17.1% with a maximum brightness (L max) of 27 000 cd/m2. BAC host material 6a exhibited better performance compared to that of commercial host 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) and 4,4′,4″-tris(carbazol-9-yl)triphenylamine. The BAC 6a host was also found to be compatible with orange, yellow, and blue phosphorescent emitters, which displayed PEs of 31.9, 21.4, and 14.1 lm/W, respectively, at a brightness of 100 cd/m2. Notably, the green PhOLED with donor–acceptor-based host 6a exhibited 23% roll-up in CE while moving from 100 to 1000 cd/m2. The enhancement of the performance of the green PhOLED is attributed to higher singlet and triplet energies of host 6a compared to that of the utilized green emitter tris(2-phenylpyridine)iridium(III), leading to effective host–guest energy transfer and the ability to form efficient excitons in the host–guest matrix, thus enhancing the OLED performance. Thus, BAC 6a has commercial potential as a suitable host material for the fabrication of efficient multicolor PhOLEDs.

Synthesis of fluorescent aromatic species via ring transformation of α-pyranones and their application in OLEDs, chemosensors, and cell imaging

“…50 Goel and coworkers were able to successfully design and synthesize several non-planar small D-A organic molecules to inhibit p-p interactions, making them feasible candidates for use as hole transporting materials in the fabrication of OLEDs. 45,[51][52][53][54][55][56] These molecules have a non-planar conformation with a push-pull system including an amine donor and a nitrile acceptor. The presence of cyano group reduces the LUMO energy level whilst the amino functionality increases the HOMO energy level of the molecule, hence decreasing the HOMO-LUMO energy gap and facilitating hole transport in the film.…”

“…81 The most recent accomplishment of Goel's group is the development of biarylcarbazole derivatives as host materials for the fabrication of phosphorescent organic light-emitting diodes. 56 Carbazole derivatives with D–A appendages were synthesised through the reaction of 6-aryl-3-cyano-4-piperidin-1-yl-2 H -pyran-2-one 11 with 1-(9-ethyl-9 H -carbazol-3-yl)ethan-1-one 54 using NaH in dry DMF at room temperature for a duration of 3–4 h (Scheme 16). Phenyl, naphthyl, thienyl, and furanyl moieties were tolerated at the C-6 position of the pyranone ring.…”

Utilization of the through-space effect to design donor–acceptor systems of pyrrole, indole, isoindole, azulene and aniline

“…6 D-A systems have found widespread application in organic photovoltaic devices. 7 Many studies have recently been undertaken to characterize the mechanisms of D-A based charge-transfer processes in optoelectronic systems such as solar cells, light-emitting diodes (LEDs), organic photovoltaics (OPVs), field-effect transistors (FETs), conducting polymers, and so on. [8][9][10] Appropriate substituents are used to fine tune the donating effect of the D and the accepting effect of the A.…”

Three-Dimensional Anisotropic Carrier Mobility and Structure–Property Relationships for [1]Benzothieno[3,2-b][1]benzothiophene Derivatives: A Theoretical Study

“…The design and exploitation of organic semiconductor materials has been an emerging and continuously growing research area in organic (opto)electronics on account of their excellent optoelectronic properties in organic optoelectronic devices, for example, organic photovoltaic cells, 1,2 organic light-emitting diodes, 3,4 and organic field-effect transistors. 5,6 Although the organic semiconductor may exhibit lower electrical performance in comparison with inorganics such as amorphous or crystalline silicon, it is considered a promising organic semiconducting material, which could compete with inorganic semiconductors on applications that require light weight, low cost, mechanical flexibility, easy fabrication, and large-area production.…”

“…The design and exploitation of organic semiconductor materials has been an emerging and continuously growing research area in organic (opto)­electronics on account of their excellent optoelectronic properties in organic optoelectronic devices, for example, organic photovoltaic cells, , organic light-emitting diodes, , and organic field-effect transistors. , Although the organic semiconductor may exhibit lower electrical performance in comparison with inorganics such as amorphous or crystalline silicon, it is considered a promising organic semiconducting material, which could compete with inorganic semiconductors on applications that require light weight, low cost, mechanical flexibility, easy fabrication, and large-area production . Among the various organic semiconducting materials investigated so far, [1]­benzothieno­[3,2- b ]­[1]­benzothiophene ( BTBT ) and its derivatives have emerged as promising materials for the fabrication of efficient OFETs since they have small reorganization energies due to their planar and rigid backbones, as well as strong intermolecular electronic couplings owing to the multiple intermolecular interactions including S···S, H···π, and S···π interactions. , In 2020, Liu et al first realized high-quality single crystals of BTBT grown on silicon dioxide substrates in ways of physical vapor transport deposition, which exhibited the maximum field-effect hole mobility of about 0.032 cm 2 ·V –1 ·s –1 .…”