11.2: Efficient Deep Blue Triplet Emitters for OLEDs

Abstract

Cyclometallated iridium carbene complexes are introduced as efficient blue triplet emitters. Quantum mechanical calculations have been used to design and to optimize this class of materials predominantely with respect to color coordinates and luminescence quantum yield. To complete the set of materials required for deep blue OLED devices we engineered suitable host and blocker materials for the use in combination with large triplet energy carbene emitters. These tailor-made materials were applied to develop deep blue electroluminescent devices with excellent efficiency.

Design Rules for Charge-Transport Efficient Host Materials for Phosphorescent Organic Light-Emitting Diodes

“…1,2 In spite of this successful commercialization, the field still has a number of open issues, such as insufficient stability 3 of OLEDs based on deep-blue (λ < 460 nm) emitters. 4,5 In a prototypical phosphorescent OLED, holes and electrons are injected from electrodes on opposite sides into transport and blocking layers that provide a balanced charge transport into an emission layer (EML). The EML itself consists of a charge-transporting organic semiconductor and an organometallic emitter that allows for triplet harvesting.…”

“…To do this, we perform a combined experimental (admittance spectroscopy) and computer simulation study of charge transport in 2,8-bis(triphenylsilyl)-dibenzofuran (BTDF), a typical electron-conducting host used in combination with hole-conducting deep-blue emitters. 5 The maximal external quantum efficiencies of such OLEDs are above 17% (see the Supporting Information for the device charateristics). The chemical structure of BTDF is shown in Figure 1c.…”

Phenylcarbazole‐Based Phosphine Oxide Host Materials For High Efficiency In Deep Blue Phosphorescent Organic Light‐Emitting Diodes

“…[7] Other than these dopant materials, carbene-type materials were reported as deep blue phosphorescent dopant materials. [8][9][10] Wide bandgap host materials are also critical for obtaining high quantum efficiency in deep blue PHOLEDs. The most well-known host material is N,N-dicarbazolyl-3,5-benzene (mCP), [11] and it was effective as a host material in the deep blue PHOLEDs due to a wide triplet bandgap of 2.9 eV.…”

En Route to High External Quantum Efficiency (∼12%), Organic True‐Blue‐Light‐Emitting Diodes Employing Novel Design of Iridium (III) Phosphors

“…[1,2] Among the related investigations, the phosphor design and fabrication of true-blue phosphorescent devices have set out an ultimate challenge, because they require the ingenious invention of volatile, higher-energy-gap phosphors with longterm stability, and the careful adjustment of guest-host energy gaps and electron-hole recombinations. [3] In efforts to search for the desired phosphors, we have long noticed that 2-pyridyl azole chromophores possess a very large intraligand p-p* energy gap. [4] Upon reacting with the third-row transition metals, they may render the isolation of a true-blue phosphors.…”

“…[11,12] The targeted phosphors, [Ir(fppz) 2 (bdp)] (1) and [Ir(fppz) 2 (dfbdp)] (2) (fppzH: 5-(2-pyridyl)-3-trifluoromethylpyrazole), bdpH: benzyldiphenylphosphine, and dfbdpH: (2,4-difluorobenzyl) diphenylphosphine), were best synthesized by a prior combination of [Ir(tht) 3 Cl 3 ] (tht: tetrahydrothiophene) with a stoichiometric amount of bdpH or dfbdpH in decahydronaphthalene, followed by treatment with the fppzH chelate in the presence of Na 2 CO 3 . This judicious choice of Ir(III) source and reaction solvent is intended to suppress the metal-hydride formation, which is commonly encountered in protic solvents such as methoxyethanol and its analogues.…”