Organic oxide/Al composite cathode in small molecular organic light-emitting diodes

Guo, Tzung‐Fang; Yang, Fuh-Shun; Tsai, Zen-Jay; Wen, Ten‐Chin; Wu, Chia-Jen; Chung, Chia-Tin

doi:10.1063/1.2266571

Cited by 15 publications

(6 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The above result probably implies that the ethylene oxide‐based thin film could work well as a buffer with Al electrodes, although the improvement on the V OC and η for P3HT:PCBM‐based OPVs made of PEO as the electrode buffer in Oh et al’s report was limited. Nevertheless, PEO‐based polymers and molecules have been successfully reported as effective electrode buffers with Al cathodes for the fabrication of high performance organic/polymer light‐emitting diodes (O/PLEDs) 30, 33–36. We attribute the debate as resulting from the different processing conditions when utilizing the PEO polymer as the electrode buffer, because it tends to absorb the moisture in the atmosphere, to crystallize, to change the thin film morphology, and – most importantly – is intrinsically an insulating polymer material.…”

Section: Introductionmentioning

confidence: 99%

The Roles of Poly(Ethylene Oxide) Electrode Buffers in Efficient Polymer Photovoltaics

Jeng

Lin

Hsu

et al. 2011

Advanced Energy Materials

Self Cite

View full text Add to dashboard Cite

The role of poly(ethylene oxide) polymer is investigated as an effective buffer with Al electrodes to markedly improve the electrode interface and enhance the open‐circuit voltage (VOC) and the power conversion efficiency (PCE, η) of poly(3‐hexylthiophene) (P3HT):[6,6]‐phenyl C61‐butyric acid methyl ester (PCBM)‐based bulk‐heterojunction (BHJ) solar cells. A unique process is developed by thermally co‐evaporating the poly(ethylene glycol) dimethyl ether (PEGDE, Mn ca. 2000) polymer with Al metal simultaneously at different ratios in vacuum (10−6 Torr) to prepare the electrode buffers. The instant formation of a carbide‐like junction at the ethylene oxide/Al interface during the thermal evaporation is of essential importance to the extraction of electrons through the Al electrode. The performance of P3HT:PCBM‐based solar cells can be optimized by modulating the co‐evaporation ratios of the PEGDE polymer with Al metal due to the changes in the work functions of the electrodes. The VOC and η for devices fabricated with Al electrode are 0.44 V and 1.64%, respectively, and significantly improve to 0.58 V and 4.00% when applying the PEGDE:Al(2:1)/Al electrode. This research leads to a novel electrode design – free of salts, additives, complicated syntheses, and having tunable work function – for fabricating high‐performance photovoltaic cells.

show abstract

Section: Introductionmentioning

confidence: 99%

The Roles of Poly(Ethylene Oxide) Electrode Buffers in Efficient Polymer Photovoltaics

Jeng

Lin

Hsu

et al. 2011

Advanced Energy Materials

Self Cite

View full text Add to dashboard Cite

show abstract

“…Recently, several reports indicated that device performance can be improved substantially by placing a thin layer of polymer oxide ͑surfactant͒, such as poly͑ethylene glycol͒ ͑PEG͒, on the cathode interface, [12][13][14] or by blending such materials into the active layer of devices. 15,16 This enhanced device performance is attributed to the chemical interaction between PEG and the Al cathode decreasing the electron injection barrier and contact resistance.…”

mentioning

confidence: 99%

“…15,16 This enhanced device performance is attributed to the chemical interaction between PEG and the Al cathode decreasing the electron injection barrier and contact resistance. [12][13][14][15][16] In this study, we applied this method to achieve efficient phosphorescent PLEDs. We obtained lower operating voltages and higher power efficiencies after blending PEG into the electroluminescent ͑EL͒ layer.…”

mentioning

confidence: 99%

Single-layer triplet white polymer light-emitting diodes incorporating polymer oxides: Effect of charge trapping at phosphorescent dopants

Chen

Chien

Chen

2009

Applied Physics Letters

View full text Add to dashboard Cite

This paper describes the effects of charge trapping on the device performances of triplet polymer light-emitting diodes (PLEDs) after the cathode contact had been improved through the blending of poly(ethylene glycol) (PEG) into the active layer. The external quantum efficiency (EQE) was enhanced when the dopant tended to trap electrons. In contrast, we observed no EQE enhancement for the device featuring a hole-trapping dopant. Because PEG promoted electron injection, more electrons were trapped in the triplet molecules, thereby enhancing the probability of recombination. Finally, after incorporating PEG, we further achieved white PLEDs exhibiting both high EQE and high power efficiency.

show abstract

“…Guo et al reported that high performance polymer and small molecule OLEDs with an organic oxide, poly(ethylene glycol) dimethyl ether (PEGDE). Because PEGDE can be evaporated at low temperature compared to other inorganic insulators and improves the device performance as much as the inorganic electron injection layers, it could be a good candidate for an organic electron injection layer [15][16][17]. In this study, the performance of PVK based PLEDs is improved by using PEO/Ca/Al cathode.…”

mentioning

confidence: 83%

Polymer light-emitting devices using poly(ethylene oxide) as an electron injecting layer

Rao

Huang

et al. 2010

Nano-Micro Lett

View full text Add to dashboard Cite

The performance of polymer light emitting devices (PLEDs) based on polyvinyl carbazole (PVK) is improved by introducing a nanoscale interfacial thin layer, made of poly(ethylene oxide) (PEO), between the calcium cathode and the PVK emissive layer. It is believed that the PEO layer plays a key role in enhancing the device performance. In comparison to the device with Ca/Al as the cathode, the performance of the PLED with PEO/Ca/Al cathode, including the driving voltage, luminance efficiency is significantly improved. These improvements are attributed to the introduction of a thin layer of PEO that can lower the interfacial barrier and facilitate electron injection. Polymer light-emitting diodes (PLEDs) have attracted much interest worldwide since their discovery by Friend and co-workers in 1990 [1]. Engineering of the polymer-electrode interfacial properties is crucial to achieve balanced hole and electron injection for high efficiency operations. Low work function metals, such as calcium or barium are widely used as a cathode to facilitate electron injection [2][3][4][5][6][7][8]. These metals are very sensitive to moisture and oxygen and form detrimental quenching sites at areas near the interface between the electroluminescent (EL) layer and the cathode. In addition, metal ions formed at the metal/organic interface tend to migrate into the EL layer, thus, affecting the long term stability of devices [9]. To circumvent these problems, it is desirable to use high work-function metals (such as Al, Ag, or Au) as the cathode because of their better environmental stability and the simplicity of their device fabrication. To improve electron injection from high-work-function metals into the emitting layer, numerous approaches have been attempted [10,11]. For example, by inserting a thin layer of lithium fluoride, or cesium fluoride, between Al and the light emitting layer, the electron-injection ability could be significantly improved [10][11][12]. It was shown by the Cao et al. that the insertion of organic surfactant molecules between Al and the EL polymer could improve device performance up to the level obtained by low-work function metal cathode [11]. Li et al. reported that effective electron injection can be achieved by the insertion of an ultrathin aluminum oxide layer between the Al and the emitting layer [13]. Lee et al. reported that polystyrene sodium sulfonate inserted between MEH-PPV and Al significantly improves electron injection [14]. Guo et al. reported that high performance polymer and small molecule OLEDs with an organic oxide, poly(ethylene glycol) dimethyl ether (PEGDE). Because PEGDE can be evaporated at low temperature compared to other inorganic insulators and improves the device performance as much as the inorganic electron injection layers, it could be a good candidate for an organic electron injection layer [15][16][17]. In this study, the performance of PVK based PLEDs is improved by using PEO/Ca/Al cathode. When a thin PEO (5 nm) buffer layer is introduced between the PVK emissive layer an...

show abstract

Organic oxide/Al composite cathode in small molecular organic light-emitting diodes

Cited by 15 publications

References 19 publications

The Roles of Poly(Ethylene Oxide) Electrode Buffers in Efficient Polymer Photovoltaics

The Roles of Poly(Ethylene Oxide) Electrode Buffers in Efficient Polymer Photovoltaics

Single-layer triplet white polymer light-emitting diodes incorporating polymer oxides: Effect of charge trapping at phosphorescent dopants

Polymer light-emitting devices using poly(ethylene oxide) as an electron injecting layer

Contact Info

Product

Resources

About