Photophysics of Pt-porphyrin electrophosphorescent devices emitting in the near infrared

Abstract

The triplet annihilation dynamics of near infrared organic light-emitting devices are studied with peak electrophosphorescence at a wavelength of 772nm using a platinum-porphyrin derivative Pt(II)-tetraphenyltetrabenzoporphyrin as dopant. Both the photoluminescent decay transients of the thin films and the quantum efficiency versus current density characteristics of devices using tris(8-hydroxyquinoline) aluminum or 4,4′-bis(N-carbazolyl)biphenyl (CBP) as hosts are fitted by a model based on triplet-triplet annihilation. When the phosphor is codoped with Ir(III) bis(2-phenyl quinolyl-N,C2′) acetylacetonate in CBP, the quantum efficiency is enhanced, and the observed decrease of efficiency at high current densities is explained by field-induced charge pair dissociation. The external quantum efficiency has a maximum of (8.5±0.3)%, decreasing to (5.0±0.3)% at 1mA∕cm2.

Rational Design of Charge‐Neutral, Near‐Infrared‐Emitting Osmium(II) Complexes and OLED Fabrication

“…The full width at half maximum (FWHM) for EL of 1 and 4 are 144 nm and 142 nm, respectively, which are greater than the FWHM of most Pt(II) based, NIR emitting phosphors. [11] The larger FWHM should be due to the lack of pp stacking interaction existing in planar Pt(II) phosphors that may further strengthen the rigidity of the chelating chromophores.…”

“…[8a,10] Most notably, NIR devices with electroluminescence at l ¼ 772 nm and maximum external quantum efficiency (EQE) of over 8.5% have been reported for the tetrabenzoporphyrin Pt(II) phosphor in 4,4 0 -bis(N-carbazolyl)biphenyl (CBP) and with 2, as an exciton blocking (EBL) and electron transport layer (ETL). [11] In this article, as the continuation of our efforts to develop efficient phosphorescent materials for OLED applications, [12] we report new Os(II) complexes with highly conjugated isoquiniolinyl triazolate chelate to obtain phosphors that shine at the longer wavelength region. It is particularly notable that these Os(II) phosphors use their lower energy MLCT contribution to further red shift the emission.…”

Near-IR organic light emitting diodes based on porphyrin compounds

“…Fully organic emitters however have been shown to combine reasonable quantum efficiencies with high current densities and do not share the same toxicity concerns as nanoparticles. Among small molecule organic emitters for OLEDs, porphyrins have attracted particular attention [7][8][9][10][11][12][13]. Emission from these porphyrins at room temperature is known to originate from the singlet excited states which make them appropriate for use in fluorescence OLEDs for applications in displays and telecommunications [14,15].…”

Near Infrared Fluorescent and Phosphorescent Organic Light-Emitting Devices

“…Existing NIR OLEDs are primarily based on lanthanide complexes [1,[4][5], but they generally have very low external quantum efficiencies (EQE~0.1%) because of the inherent low efficiency of emission from these complexes. Only recently were high efficiency NIR OLEDs reported, in which peak emission at λ ≈ 770 nm and a maximum EQE up to 8.5% were achieved using a phosphorescent Pt-porphyrin complex [6]. Nonetheless, alternative materials and devices that exhibit longer wavelength (λ > 800 nm) emissions with high efficiencies are still needed.…”

“…High efficiencies can be achieved when they are used as the phosphorescent emitters in OLEDs [6]. High efficiencies can be achieved when they are used as the phosphorescent emitters in OLEDs [6].…”