Microcavity two-unit tandem organic light-emitting devices having a high efficiency

Cho, Ting‐Yi; Lin, Chong; Wu, Chung‐Chih

doi:10.1063/1.2185077

Cited by 179 publications

(119 citation statements)

References 13 publications

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“…Adversely, the Stokes shift is increased and the EL peaks are broadened. Presently, most of the commercially available OLEDs employ a colour filter [96,97] to produce a pure blue emission. In this context, Hatakeyama et al overcame these issues by establishing a new design way to minimize ∆E ST of the materials without enlarging of the FL peaks.…”

Section: Triarylborane Emittersmentioning

confidence: 99%

Thermally Activated Delayed Fluorescence Emitters for Deep Blue Organic Light Emitting Diodes: A Review of Recent Advances

et al. 2018

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Organic light-emitting diodes offer attractive perspectives for the next generation display and lighting technologies. The potential is huge and the list of potential applications is almost endless. So far, blue emitters still suffer from noticeably inferior electroluminescence performances in terms of efficiency, lifespan, color quality, and charge injection/transport when compared to that of the other colors. Emitting materials matching the NTSC standard blue of coordinates (0.14, 0.08) are extremely rare and still constitutes the focus of numerous academic and industrial researches. In this context, we review herein the recent developments on highly emissive deep-blue thermally activated delayed fluorescence emitters that constitute the third-generation electroluminescent materials.

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Section: Triarylborane Emittersmentioning

confidence: 99%

Thermally Activated Delayed Fluorescence Emitters for Deep Blue Organic Light Emitting Diodes: A Review of Recent Advances

et al. 2018

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“…10,11 However, the efficiency roll-off ͑the decrease of efficiency with increasing current density͒ occurs at much lower luminance than required in displays or solid-state lighting. The roll-off of the quantum efficiency is one of the most significant problems facing electrophosphorescent devices and its origin was attributed to the triplet-triplet annihilation coming from long lifetime of triplet excitons, 12,13 electric field induced dissociation of excitons, 14 and tripletpolaron annihilation.…”

mentioning

confidence: 99%

Low roll-off of efficiency at high current density in phosphorescent organic light emitting diodes

Kang¹,

Lee²,

Park³

et al. 2007

Applied Physics Letters

206

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The authors demonstrate that the reduction of quantum efficiency with increasing current density in phosphorescent light emitting diodes ͑PhOLEDs͒ is related to the formation of excitons in hole transporting layer based on the analysis of emission spectra and exciton formation zone. Low roll-off of efficiency in a PhOLED was achieved using dual emitting layers ͑D-EMLs͒ by confining the exciton formation near the interface between the emitting layers. The external quantum efficiency was maintained almost constant up to 22 mA/ cm 2 ͑10 000 cd/ m 2 ͒ by adopting the D-EMLs in Ir͑ppy͒ 3 based PhOLEDs, resulting in high external quantum efficiency ͑ ext = 13.1% ͒ at high luminance. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2745224͔ Phosphorescent organic lighting emitting diodes ͑PhOLEDs͒ have received considerable attention due to their ability of highly efficient emission compared with fluorescent OLEDs.1-4 Through harvesting of both singlet and triplet excitons, the external quantum efficiency ͑ ext ͒ of PhOLEDs has reached above 20% by using the optimized material systems, 5-7 p-i-n structures, 8,9 and microcavity structures.10,11 However, the efficiency roll-off ͑the decrease of efficiency with increasing current density͒ occurs at much lower luminance than required in displays or solid-state lighting. The roll-off of the quantum efficiency is one of the most significant problems facing electrophosphorescent devices and its origin was attributed to the triplet-triplet annihilation coming from long lifetime of triplet excitons, 12,13 electric field induced dissociation of excitons, 14 and tripletpolaron annihilation. 12,13 In this letter, we report that the roll-off of the quantum efficiency with an increasing current density is related to the exciton formation in the hole transporting layer ͑HTL͒. Analysis of the steady state emission spectra indicated that the significant portion of the efficiency reduction is originated from the more and more exciton formation in the HTL with increasing current density. Based on the results, we fabricated devices with double emitting layers ͑D-EMLs͒ in order to confine the exciton formation in the emitting layers. The external quantum efficiency ͑ ext ͒ was maintained constant up to 22 mA/ cm 2 ͑10 000 cd/ m 2 ͒ by adopting the D-EMLs in Ir͑ppy͒ 3 based PhOLEDs, resulting in high external quantum efficiency at high luminescence compared to the devices with single emitting layer ͑S-EML͒. The OLEDs with D-EMLs show significantly lower roll-off of efficiency ͓ ext = 13.1% at 10 000 cd/ m 2 ͑22 mA/ cm 2 ͔͒ than conventional S-EML OLEDs ͓ ext = 7.8% at 5400 cd/ m 2 ͑20 mA/ cm 2 ͒, and 6.9% at 10 000 cd/ m 2 ͑40 mA/ cm 2 ͔͒. The OLEDs were fabricated by thermal evaporation onto a cleaned glass substrate precoated with indium tin oxide ͑ITO͒ without breaking the vacuum. Prior to organic layer deposition, ITO substrates were exposed to UV-ozone flux for 10 min following degreasing in aceton and isoprophyl alcohol. All organic layers were grown by thermal evaporation at the...

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“…Under these conditions the emissive layer lies at the antinode of the electric fields as found in earlier studies of tandem OLEDs. 5 As discussed in Sec. 2.3, for the single cavity OLED (Fig.…”

Section: Results With the Scattering Matrix Simulationmentioning

confidence: 97%

“…Utilizing multiple wavelength emission from a cavity has been demonstrated to be a viable solution for achieving white light OLEDs. [1][2][3][4] Tandem OLEDs are formed by combining in series single units 5,6 separated by a charge generation layer (CGL), analogous to tandem solar cells. Tandem OLEDs with different emitting species in each repeat unit can generate multiple wavelength emission, which can be combined to generate white light.…”

Section: Introductionmentioning

confidence: 99%

“…OLED architectures combining microcavities with tandem structures have been shown 3,5 to yield strong enhancement in efficiency. This paper describes the results of simulations of the emission from microcavity tandem OLEDs, using rigorous finite element and Fourier space solutions of Maxwell's equations, and compares them to experimental results.…”

Section: Introductionmentioning

confidence: 99%

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Simulations of emission from microcavity tandem organic light-emitting diodes

Biswas

Zhao

et al. 2011

J. Photon. Energy

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Abstract. Microcavity tandem organic light-emitting diodes (OLEDs) are simulated and compared to experimental results. The simulations are based on two complementary techniques: rigorous finite element solutions of Maxwell's equations and Fourier space scattering matrix solutions. A narrowing and blue shift of the emission spectrum relative to the noncavity single unit OLED is obtained both theoretically and experimentally. In the simulations, a distribution of emitting sources is placed near the interface of the electron transport layer tris(8-hydroxyquinoline) Al (Alq 3 ) and the hole transport layer (N,N -bis(naphthalen-1-yl)-N,N

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Microcavity two-unit tandem organic light-emitting devices having a high efficiency

Cited by 179 publications

References 13 publications

Thermally Activated Delayed Fluorescence Emitters for Deep Blue Organic Light Emitting Diodes: A Review of Recent Advances

Thermally Activated Delayed Fluorescence Emitters for Deep Blue Organic Light Emitting Diodes: A Review of Recent Advances

Low roll-off of efficiency at high current density in phosphorescent organic light emitting diodes

Simulations of emission from microcavity tandem organic light-emitting diodes

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