In research on small-molecule organic light-emitting diodes (OLEDs), the molecular orientation in vacuum-deposited amorphous films has been disregarded for around 20 years, and its effects on device performance have not been sufficiently discussed at the microscopic level. Only recently have the intermolecular interaction and subsequent horizontal molecular orientation in OLEDs been investigated and reported. In this article, an overview of the recent studies on molecular orientation in OLEDs is presented. The general properties of molecular orientation of OLED materials are shown, and its significant effects on the electrical and optical properties of devices are discussed to understand device physics and improve the future performance and reliability of OLEDs.

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Molecular orientation in small-molecule organic light-emitting diodes

Novel tricarbazole compounds are provided. By appropriately selecting the nature of the tricarbazole substituents, compounds with appropriate HOMO and LUMO energies can be obtained for use as materials in a secondary hole transport layer.

Organic Electroluminescent Materials and Devices

An organic light emitting device is provided. The device has an anode, a cathode, and an emissive layer disposed between the anode and the cathode. The emissive layer further comprising an emissive material having the structure: (I) M may be a metal having an atomic weight greater than 40. R3 may be a substituent having a Hammett value less than about -0.17, between about -0.15 and 0.05, or greater than about 0.07. R5 may be H or any substituent. A may be a 5 or 6 member heteroaryl ring system. 'm' may be at least 1. 'n' may be at least zero. (X-Y) may be an ancillary ligand. The emissive material itself is also provided. The emissive material may have improved stability, and may provide a saturated blue emission.

Organic light-emitting materials and devices

In this review article, the important features (optical, thermal and electrochemical) of triphenylamine (TPA) based organic hole transport materials (HTMs) in accordance with their structural diversities are discussed from their evolution to recent advancements. The literature here covers past and ongoing work mostly relevant to HTMs used in DSSCs and PSCs. Besides the good optical properties and high hole mobility, the stability of the amorphous state of the HTM layer is a crucial factor in the commercialization of PSCs. The stability of the amorphous glassy state of HTMs is defined by an important physical parameter, i.e., the glass transition temperature (Tg) which is discussed on the basis of the molecular structure of HTMs.

A review on triphenylamine (TPA) based organic hole transport materials (HTMs) for dye sensitized solar cells (DSSCs) and perovskite solar cells (PSCs): evolution and molecular engineering

Compounds comprising phosphorescent metal complexes comprising cyclometallated imidazo[1,2-f]phenanthridine and diimidazo[1,2-a:1′,2′-c]quinazoline ligands, or isoelectronic or benzannulated analogs thereof, are described. Organic light emitting diode devices comprising these compounds are also described.

Metal Complexes of Cyclometallated Imidazo[1,2-f]phenanthridine and Diimidazo[1,2-a:1',2'-c]quinazoline Ligands and Isoelectronic and Benzannulated Analogs Thereof

In this study, the authors show an empirical guideline for designing hole transport materials (HTMs) that suppress rises in driving voltage even with a few hundred nanometer thick film in the organic light emitting diodes (OLEDs). In a device structure of indium tin oxide (110nm)/hole transport layer (HTL) (Xnm)∕4,4′-N,N′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (10nm)/tris-(8-hydroxyquinoline)aluminum (Alq3) (50nm)∕MgAg (100nm)∕Ag (10nm), the authors compared electroluminescence characteristics of the OLEDs having a thin-film HTL (X=50nm) and a thick-film HTL (X=300nm) using 13 kinds of HTMs. They observed a closed correlation between suppression of the driving voltage and the HTMs’ thermal characteristics. Highly thermally stable HTMs resulted in a small increase in the driving voltage.

Tetsuzou Miki

Papers

Material design of hole transport materials capable of thick-film formation in organic light emitting diodes