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

Abstract

The use of blue phosphorescent emitters in organic light-emitting diodes (OLEDs) imposes demanding requirements on a host material. Among these are large triplet energies, the alignment of levels with respect to the emitter, the ability to form and sustain amorphous order, material processability, and an adequate charge carrier mobility. A possible design strategy is to choose a π-conjugated core with a high triplet level and to fulfill the other requirements by using suitable substituents. Bulky substituents, however, induce large spatial separations between conjugated cores, can substantially reduce intermolecular electronic couplings, and decrease the charge mobility of the host. In this work we analyze charge transport in amorphous 2,8-bis(triphenylsilyl)dibenzofuran, an electron-transporting material synthesized to serve as a host in deep-blue OLEDs. We show that mesomeric effects delocalize the frontier orbitals over the substituents recovering strong electronic couplings and lowering reorganization energies, especially for electrons, while keeping energetic disorder small. Admittance spectroscopy measurements reveal that the material has indeed a high electron mobility and a small Poole−Frenkel slope, supporting our conclusions. By linking electronic structure, molecular packing, and mobility, we provide a pathway to the rational design of hosts with high charge mobilities.

Cost-Effective Force Field Tailored for Solid-Phase Simulations of OLED Materials

“…of samples with dimensions of about 10 4 − 10 6 nm 3 . Note that the most popular ones are optimized for other purposes 26 and that, to date, the literature appears to be not only scarce of efforts for obtaining the first objective, exception made for the notable work of Andrienko, Lennartz, Wenzel and collaborators, 19,20,24,[27][28][29][30] but also almost absent of attempts of reducing the computational cost via the derivation of simpler potentials.…”

“…The torsional parameters V n , n, γ n were borrowed from the AMBER95 dataset for what concerns the rigid ones, e.g. torsions involving carbon atoms belonging to the same aromatic ring, while soft, anharmonic torsions were here parametrized with quantum chemistry calculations 29,41,44 at PBE0-D3(BJ)/def2-TZVP level. In practice, only three types of torsion were reworked: phenyl-phenyl, phenylcarbazole, and the improper torsion involving the out-of-plane vibration of sp 2 nitrogen; the phenyl-nitrogen torsion in TPA being modeled with standard parameters, as it is dominated by steric repulsion which confers it a propeller-like structure.…”

Structure–property relationship of 4-substituted-spirobifluorenes as hosts for phosphorescent organic light emitting diodes: an overview

“…Using an insulating heteroatom is also an efficient strategy to obtain high E T materials with short π-conjugated pathway. Thus, silicium (silane), [44][45][46][47][48][49] and phosphoryl group (P=O), 40,44,47,[50][51][52][53] may act as an effective breaking point of the π-conjugation between the main core of the molecule and the outer groups linked to the heteroatom (phenyl for example in the case of the efficient electron transporting diphenylphosphine oxide unit). More recently, another efficient molecular design based on a π-conjugation breaking induced by an insulating spiro bridge (Called Donor-Spiro-Acceptor design) has been also successfully introduced in literature.…”

Benzimidazobenzothiazole‐Based Bipolar Hosts to Harvest Nearly All of the Excitons from Blue Delayed Fluorescence and Phosphorescent Organic Light‐Emitting Diodes

“…[11,10a] However,s uch spacers can lead to poor charge mobility in organic conjugated materials. [12] Herein, we report an acceptor unit, benzimidazobenzothiazole (BID-BT), featuring ar igid configuration with benzimidazole as an electron-deficient moiety to aid electron transport, and benzothiazole as the backbone linked by at ertiary nitrogen atom as ab ridge.T he tertiary nitrogen bridge maintains not only rigidity but also the high triplet energy of the BID-BT ring. We synthesized BID-BT derivatives 2,9-di(9H-carbazol-9-yl)benzo [d]benzo [4,5]imidazo [2,1-b]thiazole (29Cz-BID-BT) and 3,9-di(9H-carbazol-9-yl)benzo-[d]benzo [4,5]imidazo [2,1-b]thiazole (39Cz-BID-BT) as host materials for blue TADF and phosphorescent OLEDs.…”