Abstract
The excellent contrast ratio, visibility, and advantages in producing thin and light displays let organic light emitting diodes change the paradigm of the display industry. To improve future display technologies, higher electroluminescence efficiency is needed. Herein, the detailed study of the non-radiative decay mechanism employing density functional theory calculations is carried out and a simple, general strategy for the design of the ancillary ligand is formulated. It is shown that steric bulk properly directed towards the phenylisoquinoline ligands can significantly reduce the non-radiative decay rate.
Highlights
The excellent contrast ratio, visibility, and advantages in producing thin and light displays let organic light emitting diodes change the paradigm of the display industry
As small changes in emission characteristics often exacerbate the efficiency drop, possible solutions considered contemplating host-dopant combinations for better orientation alignment of transition dipole moments[6,7], or decorating the emitters with functional groups without too severely modifying the chromophore scaffolds[8], but a decisive advance has not been achieved to date
The non-radiative mechanism of heteroleptic Ir(III)-dopants. It is well-established that the desired photophysical behavior relies on metal-to-ligand charge transfer (MLCT) excited states involving the π* orbitals of the ppy type ligand
Summary
The excellent contrast ratio, visibility, and advantages in producing thin and light displays let organic light emitting diodes change the paradigm of the display industry. The detailed study of the non-radiative decay mechanism employing density functional theory calculations is carried out and a simple, general strategy for the design of the ancillary ligand is formulated. A new family of red dopants with longer wavelengths are needed, but simple energy gap law considerations explain that efficiency lowering due to increased non-radiative decay is inevitable[4,5]. A potential solution is to employ heteroleptic Ir-complexes carrying three bidentate ligands, of which two are mainly responsible for the luminescence, and one is a supporting ancillary ligand that is not directly involved in the phosphorescence. Ir(III)-complexes carrying bidentate phenylpyridine (ppy) type ligands emerged as an important class of emitters[10], and a typical ancillary ligand is an acetylacetone (acac) derivative[2]. Whereas the DFT models are not necessarily accurate, they provide exact information that is easy to interpret and conceptualize
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