Energy structures and chemical reactions at the Al∕LiF∕Alq3 interfaces studied by synchrotron-radiation photoemission spectroscopy

Wu, Chih-I; Lee, Guan-Ru; Pi, Tun‐Wen

doi:10.1063/1.2135376

Cited by 64 publications

(33 citation statements)

References 18 publications

(11 reference statements)

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“…Note that pure Alq 3 thin films with cathode metal of Al and Au do not show any significant ESR signal. Previous works have shown that LiF can be decomposed into Li atoms through a reaction 3LiF + Al = AlF 3 + Li, and that the formation of n-doped Alq 3 by released Li atoms is the main mechanism of the doping process [13,14]. Ref.…”

Section: Resultsmentioning

confidence: 99%

Study on n-type Doped Electron-Transporting Layers in OLEDs by Electron Spin Resonance

Son

Shimoi

Marumoto

2014

Molecular Crystals and Liquid Crystals

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We present an electron spin resonance (ESR) study of Cs 2 CO 3 and LiF doped tris(8-hydroxyquinoline) aluminum (Alq 3 ) thin films. The g values of the Cs 2 CO 3 and LiF doped Alq 3 thin films were obtained as 2.0040 and 2.0028, repectively. The g value of the LiF doped film was very close to a theoretically calculated one for an isolated Alq 3 radical anion, while Cs 2 CO 3 doped film showed a large g shift. This feature can be explained by large spin-orbit interaction caused by heavy Cs atoms. While doping of Cs 2 CO 3 did not showed cathode-metal (Al and Au) dependence, LiF doping required Al as cathode.

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Section: Resultsmentioning

confidence: 99%

Study on n-type Doped Electron-Transporting Layers in OLEDs by Electron Spin Resonance

Son

Shimoi

Marumoto

2014

Molecular Crystals and Liquid Crystals

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“…This result is attributed to the energy level shift in the organic metal interface caused by chemical reaction between Alq 3 / LiF after Al deposition. 23 The band alignment at the interface will be altered, which helps the carriers transporting between the active materials and electrodes. Comparing the characteristics of device G, H, and I, it indicates that V oc is dominated by the LiF layer.…”

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confidence: 99%

Effects of cathode buffer layers on the efficiency of bulk-heterojunction solar cells

Chang

Lin

Chiou

et al. 2010

Applied Physics Letters

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The effects of cathode buffer layers on the bulk-heterojunction solar cells are investigated. Comparing with the device without buffer layer, obvious enhancements of Voc from 0.38 to 0.65 V and fill factor from 44% to 63% have been achieved by using 2 nm bathocuproine layer, which make the efficiency of the devices improved from 1.63% to 4.11%. Alternatively, lithium fluoride and/or tris(8-hydroxyquinolinato) aluminum were also introduced for clarification purpose. X-ray photoelectron spectroscopy study indicates that the degradation caused by the outer diffusion of carbon from active layers plays a crucial role in the device performance.

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“…37 More direct evidence of the existence of Li + in such a system has been demonstrated by Wu et al with synchrotron radiation photoemission spectroscopy. 38 At the same time, with the presence of LiF insertion layer, the reaction is much less destructive than that in Al/Alq3 interface. However, at Au/LiF/Alq interface, our XPS results (not shown) suggest that the core level positions of pristine Alq are fully recovered at the final stage, leading to the overall "flat-band" situation in the interface region as shown in the inset of Fig.…”

Section: Lif Insertion Layer Between Metal Cathode and Alq Filmmentioning

confidence: 99%

Interface study of insertion layers in organic semiconductor devices

Ding

Gao

2009

SPIE Proceedings

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Inserting an ultra-thin interlayer has been an important means in modifying the performance of organic semiconductor devices. Using photoemission and inverse photoemission spectroscopy (UPS, XPS and IPES), we have investigated the electronic structure of a number of insertion layers widely used in organic semiconductor devices. We found that inserting alkali metal compound thin layers such as LiF between the electron transport layer (ETL) and the cathode can induce energy level shift in the ETL that reduces the electron injection barrier. The reduction is attributed to the release of the alkali metal that n-doped the ETL, and as such it depends on the cathode material deposited on top of the insertion layer. For thin metal oxide insertion layers, such as MoO 3 , between the anode and the hole transport layer (HTL), reduction of the hole injection barrier is also observed. This reduction, however, is due to the large workfunction of the oxide that subsequently moves the highest occupied molecular orbital (HOMO) toward the anode Fermi level. Effects of other insertion layers, such as metal insertion layer in organic bistable device (OBD) and organic insertion layer in bipolar organic thin film transistors (OTFT) will also be discussed.

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Energy structures and chemical reactions at the Al∕LiF∕Alq3 interfaces studied by synchrotron-radiation photoemission spectroscopy

Cited by 64 publications

References 18 publications

Study on n-type Doped Electron-Transporting Layers in OLEDs by Electron Spin Resonance

Study on n-type Doped Electron-Transporting Layers in OLEDs by Electron Spin Resonance

Effects of cathode buffer layers on the efficiency of bulk-heterojunction solar cells

Interface study of insertion layers in organic semiconductor devices

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