High-efficiency tandem organic light-emitting diodes

The authors have demonstrated efficient polymeric tandem organic light-emitting diodes (OLEDs) with a self-organized interfacial layer, which was formed by differences in chemical surface energy. Hydrophilic poly(styrene sulfonate)-doped poly(3,4-ethylene dioxythiophene) (PEDOT:PSS) was spin coated onto the hydrophobic poly(9,9-dyoctilfluorene) (PFO) surface and a PEDOT:PSS bubble or dome was built as an interfacial layer. The barrier heights of PEDOT:PSS and PFO in the two-unit tandem OLED induced a charge accumulation at the interface in the heterojunction and thereby created exciton recombination at a much higher level than in the one-unit reference. This effect was confirmed in both the hole only and the electron only devices.

mentioning

confidence: 99%

mentioning

confidence: 99%

Polymeric tandem organic light-emitting diodes using a self-organized interfacial layer

Ryu

Kim

Noh

et al. 2008

“…This result shows that the introducing of LiF/Ca/C 60 / NPB:MoO 3 /MoO 3 -based ICL could effectively reduce the operation voltage for tandem devices at a certain luminance and apparently promotes the enhancement in power efficiency, which is superior to the reported works previously. 4 Figure 5 depicts the accelerated lifetime decay curves for devices A, C, M, and N. The half-lifetime under the brightness of 5000 cd/m 2 is about 2.6, 11.9, 11.5, and 11.8 hours for devices A, C, M, and N, respectively. We attribute the obvious improvement in tandem devices' reliability to the efficient electroluminescence under relatively low current density at a certain luminance.…”

mentioning

confidence: 99%

“…2,3 Tandem organic light emitting devices (OLEDs) have received considerable attention recently because of their high current efficiency and long lifetime. [4][5][6] Tandem OLED generally consists of two or more emissive units. Thus, in principle, the electroluminescence (EL) intensity of the tandem device can linearly increase with the number of emissive units.…”

mentioning

confidence: 99%

C60/N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine:MoO3 as the interconnection layer for high efficient tandem blue fluorescent organic light-emitting diodes

Yang

et al. 2013

The high efficient tandem blue fluorescent organic light emitting diodes (OLEDs) with the transparent interconnection layer (ICL) of fullerence (C 60 )/Molybdenum oxide (MoO 3 )-doped N,N 0 -bis(1-naphthyl)-N,N 0 -diphenyl-1,1 0 -biphenyl-4,4 0 -diamine (NPB) were presented. A stack consisting of 0.5 nm of LiF and 1 nm of Ca, which is located from C 60 to adjacent electron transporting layer is used as an electron injection layer. The experiment results indicate that the luminance of the tandem device is basically equal to that of the traditional single-unit device, but the current density of the tandem device is much less than that of the single-unit device under a same luminance. The current efficiency and the maximal power efficiency of tandem device with LiF/Ca/C 60 /NPB:MoO 3 /MoO 3 -based interconnection layer have been approximately enhanced by 250% and 126%, respectively. In addition, we also analyze that the mechanism of the efficiency enhancement is ascribed to the effective charge separation and transport of the ICL in tandem OLEDs. V C 2013 AIP Publishing LLC. [http://dx

“…[1][2][3][4] Considering the microcavity effect, OLEDs can be roughly categorized into two types, i.e., weak microcavity OLEDs and strong microcavity OLEDs. Conventional bottom emitting OLEDs are weak microcavity devices, while OLEDs with distributed Bragg reflectors or two metallic electrodes are considered as strong microcavity devices.…”

mentioning

confidence: 99%

Modifications of the exciton lifetime and internal quantum efficiency for organic light-emitting devices with a weak/strong microcavity

Chen¹,

Choy²,

Liang³

et al. 2007

A comprehensive analysis is given on the modifications of the exciton lifetime and internal quantum efficiency ͑ int ͒ for organic light-emitting devices ͑OLEDs͒. A linear relation is derived between the exciton lifetime and int , which is difficult to measure directly. The internal quantum efficiency can thus be estimated easily through the measurement of the exciton lifetime. The exciton lifetimes for OLEDs with weak or strong microcavity are studied experimentally and theoretically. The modification of the exciton lifetime is well explained through the microcavity effect and surface plasmon resonance. An excellent agreement between the experimental and theoretical results is achieved. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2819610͔Organic light-emitting devices ͑OLEDs͒ with various device configurations have been the subject of intensive research due to their applications in display and lighting. [1][2][3][4] Considering the microcavity effect, OLEDs can be roughly categorized into two types, i.e., weak microcavity OLEDs and strong microcavity OLEDs. Conventional bottom emitting OLEDs are weak microcavity devices, while OLEDs with distributed Bragg reflectors or two metallic electrodes are considered as strong microcavity devices. Light emission properties, including the internal quantum efficiency ͑ int ͒, external quantum efficiency, exciton lifetime, and angular dependence, are distinct in the two types of OLEDs due to the Purcell effect. [5][6][7][8] Exciton lifetimes of emitters in planar dielectric microcavity structures, 9 near a partially reflecting surface, 10,11 in weak microcavity OLEDs, 12,13 and above metallic gratings 14 have been investigated either theoretically or experimentally. In this letter, a comprehensive analysis is given on the modifications of exciton lifetime for OLEDs with various device structures. A linear relation between the exciton lifetime and int will be derived, which means that int can be obtained indirectly through the measurement of exciton lifetime. In addition, we investigate both experimentally and theoretically the exciton lifetime for OLEDs with a weak or a strong microcavity.The theoretical analysis of exciton lifetime is based on a classical approach where the emitter is considered as an electric dipole running at a fixed current and with a random orientation. 6,15,16 As a consequence of Fermi's golden rule, the radiative decay rate ⌫ r ͑ ͒ at a wavelength in an OLED device is modified to 15,16 where ⌫ 0 ͑ ͒ is the radiative decay rate in the infinite medium. Here, F͑ ͒, the so-called Purcell factor, is the normalized total emission power of the electric dipole with random orientation ͑normalized by the total power of the dipole in the infinite medium͒. It should be noted that here, the emission power coupled to the metal electrode is also included in F. We consider such decay channel as radiative decay since this part of emission can potentially be coupled out from the device through, for example, patterning the substrate. 17 In addition, we typica...