Relationship between exciton recombination zone and applied voltage in organic light-emitting diodes

Hao, Jingang; Deng, Zhenbo; Shen, Yang

doi:10.1016/j.displa.2006.01.001

Cited by 6 publications

(3 citation statements)

References 14 publications

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“…Interestingly, when the applied voltage is higher than 10.0 V, the emission of BCP disappears. This phenomenon was attributed to the shift of recombination zone toward the anode because electron injection increases faster than hole injection with increasing applied voltage. , On the other hand, as shown in Figure b, evident BCP emission can be observed in device E even at very high applied voltage. This result demonstrates the faster hole penetration in device E than that in device D, thus indicating the presence of other paths of hole penetration in device E. As shown in Figure , holes transfer first from CBP to Eu(TTA) 3 phen molecules (processes 6), and then injection into the BCP layer (process 7 in Figure ) is believed to be another possible path of hole penetration in device E because of the 0.5 eV lower HOMO level of Eu(TTA) 3 phen than that of CBP .…”

Section: Resultsmentioning

confidence: 96%

Electroluminescence of Hole Block Material Caused by Electron Accumulation and Hole Penetration

et al. 2008

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In this study, we investigated the electroluminescence (EL) mechanisms and processes of hole block material in the multilayer devices with Eu(TTA)3phen (TTA = thenoyltrifluoroacetone, phen = 1,10-phenanthroline) doped CBP (4,4′-N,N′-dicarbazolebiphenyl) as the light-emitting layer (EML). First, the hole block ability of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was experimentally confirmed by comparing the EL spectra. With increasing hole injection, BCP emission emerges and increases gradually due to the increasing hole penetration from EML into the hole block layer (HBL). Interestingly, we found that BCP emission decreases gradually with decreasing electron injection, which was attributed to the decreasing electron accumulation in HBL. By analyzing the evolution of carrier distribution in EML and HBL with decreasing electron injection, we concluded that two preconditions are very important for the EL of BCP: one is the accumulation of electrons in HBL, the other is the penetration of holes from EML into HBL. In addition, we further investigated the detailed penetration processes of holes from EML into HBL, and demonstrated that the doping of Eu(TTA)3phen molecules in EML facilitates the penetration of holes because they function as ladders between CBP and BCP molecules.

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Section: Resultsmentioning

confidence: 96%

Electroluminescence of Hole Block Material Caused by Electron Accumulation and Hole Penetration

et al. 2008

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“…It was reported that the recombination zone shifts to the anode side with increased applied voltages, which results in the change of chrominance in the multilayer devices. [43] Thus, the variation in the CIE coordinate is attributed to higher operating voltages due to the hole-blocking properties of these anode buffer layers, which lead to the movement of the recombination zone away from the cathode side and closer to the anode side.…”

Section: Resultsmentioning

confidence: 99%

Tetraalkyl-substituted zinc phthalocyanines used as anode buffer layers for organic light-emitting diodes*

et al. 2020

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Two soluble tetraalkyl-substituted zinc phthalocyanines (ZnPcs) for use as anode buffer layer materials in tris(8-hydroxyquinoline)aluminum (Alq3)-based organic light-emitting diodes (OLEDs) are presented in this work. The hole-blocking properties of these ZnPc layers slowed the hole injection process into the Alq3 emissive layer greatly and thus reduced the production of unstable cationic Alq3 ( Alq 3 + ) species. This led to the enhanced brightness and efficiency when compared with the corresponding properties of OLEDs based on the popular poly-(3, 4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) buffer layer. Furthermore, because of the high thermal and chemical stabilities of these ZnPcs, a nonaqueous film fabrication process was realized together with improved charge balance in the OLEDs and enhanced OLED lifetimes.

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“…Hence, here we witness the much weaker electromer emissions over usually stronger exciton or excimer emission. The effect of recombination zone (RZ) also determines the shape of the EL spectra [37,48,49]. In this work, the presented device structure posses multiple RZs.…”

Section: (B))mentioning

confidence: 99%

Broadband white electroluminescence from a dopant-free OLED comprising pure electromer and electroplex emission

Barah,

Ray

2024

J. Phys. D: Appl. Phys.

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The utilization of multiple charge transfer (CT) complex-based emissions from a bilayer organic device is a low-cost and simple technique to realize white organic light emitting diodes (WOLEDs). In this work, a WOLED structure is presented where a planar heterojunction of 1, 1-bis ((di-4-tolylamino) phenyl) cyclohexane (TAPC) / Bis [2-(diphenylphosphino) phenyl] ether oxide (DPEPO) is employed for white-lightgeneration and thereby eliminating the blend of host and dopants which is typically used as the emissive layer in OLEDs. The WOLED exhibits a broadband emission with a full-width half maxima (FWHM) of 330 nm. A systematic investigation is carried out to interpret the origins of the red (R), yellow (Y), and blue (B) components of the spectrum. It is shown that the electroplex emission originating from TAPC/DPEPO hetero-interface is responsible for the blue emission peak at a wavelength of 488 nm. The electromer emissions from TAPC and DPEPO result in yellow and red emissions with peak intensities at wavelengths 575 nm and 670 nm, respectively. By tuning the relative intensities of the RYB components, the colour of the emitted light from the OLED can be varied and a pure white emission with the CIE coordinate of (0.34, 0.36) and colour rendering index (CRI) of 89 is demonstrated.

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Relationship between exciton recombination zone and applied voltage in organic light-emitting diodes

Cited by 6 publications

References 14 publications

Electroluminescence of Hole Block Material Caused by Electron Accumulation and Hole Penetration

Electroluminescence of Hole Block Material Caused by Electron Accumulation and Hole Penetration

Tetraalkyl-substituted zinc phthalocyanines used as anode buffer layers for organic light-emitting diodes*

Broadband white electroluminescence from a dopant-free OLED comprising pure electromer and electroplex emission

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