Photoelectron Spectroscopy of the Contact between the Cathode and the Active Layers in Plastic Solar Cells: The Role of LiF

Jönsson, Stina; Carlegrim, Elin; Zhang, Fengling; Salaneck, W. R.; Fahlman, Mats

doi:10.1143/jjap.44.3695

Cited by 111 publications

(94 citation statements)

References 40 publications

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“…The previously published IE was 5.8 eV. 56 These measurements indicate that the Fermi energy is within or very close to the LUMO band. This result is inconsistent with a typical understanding of how organic semiconductors operate and is thus most likely a measurement artifact.…”

supporting

confidence: 63%

Mixed interlayers at the interface between PEDOT:PSS and conjugated polymers provide charge transport control

et al. 2015

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Poly(3,4-ethylenedioxythiophene)-poly(styrenesulphonate) (PEDOT:PSS) is the most used organic hole injecting or hole transporting material. The hole carrying matrix PEDOT is highly doped by the acidic dopant PSS. When coated onto a substrate, PEDOT:PSS makes a highly uniform conductive layer and a thin (<5 nm) overlayer of PSS covers the air interface. Semiconducting polymer layers for organic photovoltaics or light emitting diodes are coated on top. In this article, we demonstrate that the PSS layer will mix with almost all conjugated polymers upon thermal annealing. Depending on the Fermi energy of the polymer an electrochemical reaction can take place, p-type doping the polymer at the interface between the PEDOT:PSS and the semiconducting polymer. We use chemical and spectroscopic analysis to characterize the polymer/PSS interlayer. We show that the stable and insoluble interlayer has a great effect on the charge injection and extraction from the interface. Finally we demonstrate and electronically model organic photovoltaic devices that are fabricated using these mixed interlayers.

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confidence: 63%

Mixed interlayers at the interface between PEDOT:PSS and conjugated polymers provide charge transport control

et al. 2015

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“…The work function of metallic aluminum is ~4.1 eV. Note that LiFmodified Al contacts are often used for a variety of reasons and the resulting work function of LiF-modified Al can take a range of values depending on deposition order and materials involved [31][32][33][34][35]. In all cases, however, the resulting work function will be smaller than that for clean Al, and as we will show, from an interface energetics standpoint, the work function of clean Al already is low enough to pin the PCBM/Al contact.…”

Section: Resultsmentioning

confidence: 99%

“…Note that reducing the effective work function of the Al contact by a LiF sandwich layer will not change this, only increase the interface dipole at the metal contact. The LiF layer can effect the contact in other ways, however, including preventing covalent bonding between Al and PCBM and possible defects resulting thereof [32][33][34].…”

Section: Resultsmentioning

confidence: 99%

Energy-Level Alignment at Metal–Organic and Organic–Organic Interfaces in Bulk-Heterojunction Solar Cells

Sehati

Lindell

Liu

et al. 2010

IEEE J. Select. Topics Quantum Electron.

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Abstract-Ultraviolet photoelectron spectroscopy measurements in combination with the Integer Charge Transfer model is used to obtain the energy level alignment diagrams for two common types of bulk heterojunction solar cell devices based on poly(3-hexylthiophene) or poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene) as the donor polymer and (6,6)-phenyl-C61-butric-acid as the acceptor molecule. A ground state interface dipole at the donor/acceptor heterojunction is present for both systems but the origin of the interface dipole differs, quadrupole-induced in the case of poly(2-methoxy-5-(3',7'-dimethyl-octyloxy)-1,4-phenylene vinylene) and integer charge transfer state based for poly(3-hexylthiophene). The presence of bound electron-hole charge carriers (charge transfer states) and/or interface dipoles is expected to enhance exciton dissociation into free charge carriers, reducing the probability that the charges become trapped by Coulomb forces at the interface followed by recombination.

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“…The interface layer modification on BHJ active layer/electrodes has been comprehensively carried out for the improvement of charge injection or collection, especially those due to mismatched energy levels between polymer materials and metal electrodes. [20][21][22] In order to enhance the PCE, several buffer layers have been reported to modify the interface between the active layer and metal electrodes. Many materials such as poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), molybdenum trioxide (MoO 3 ), vanadium pentoxide (V 2 O 5 ), nickel oxide (NiO 2 ), and tungsten oxide (WO 3 ) have been used as hole transport buffer layers, [23][24][25][26] and titania (TiO x ), lithium fluoride (LiF), cesium carbonate (CsCO 3 ), and zinc oxide (ZnO) have been reported for electron extraction layers [27][28][29][30] to improve the device performance.…”

mentioning

confidence: 99%

Influence of solvent treatment with fluoro compounds on the properties of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) polymer as a hole transport layer in polymer solar cells

Kumar

Shin

et al. 2014

J. Photon. Energy

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Abstract. We prepared high conducting poly (3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) by solvent additives for using as a hole transport layer (HTL) in polymer solar cells (PSCs). PEDOT:PSS films treated with fluoro compounds of hexafluoroacetone (HFA) and hexafluoroisoproponal (HFIPA) with various concentrations show a significant enhancement in electrical conductivity without compromising optical transparency. The conductivity increased from 0.2 to 1053 and 746 S∕cm after 4 vol. % HFA and 6 vol. % HFIPA treatments, respectively. The high performance of the PEDOT:PSS layer is attributed to preferential phase segregation of PEDOT:PSS with HFA and HFIPA solvent mixture treatment methods. The improved performance of PSC was dependent on the structure of organic solvents and the concentration of fluoro compounds in PEDOT:PSS solution. Using these optimized layers, conjugated PSCs with a poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5 thiophenediyl] polymer:[6,6]-phenyl-C71-butyric acid methyl esters (PCDTBT∶PC 71 BM) bulk heterojunction have been produced. The high power conversion efficiency (PCE) of 4.10% and 3.98% were observed for PEDOT:PSS films treated with 4 vol. % HFA and 6 vol. % HFIPA treatments, respectively. The obtained results show that PEDOT:PSS optimized with HFA and HFIPA organic solvents can be a very promising candidate for transparent anode buffer layer in the low cost organic solar cell devices. © The Authors.Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Photoelectron Spectroscopy of the Contact between the Cathode and the Active Layers in Plastic Solar Cells: The Role of LiF

Cited by 111 publications

References 40 publications

Mixed interlayers at the interface between PEDOT:PSS and conjugated polymers provide charge transport control

Mixed interlayers at the interface between PEDOT:PSS and conjugated polymers provide charge transport control

Energy-Level Alignment at Metal–Organic and Organic–Organic Interfaces in Bulk-Heterojunction Solar Cells

Influence of solvent treatment with fluoro compounds on the properties of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) polymer as a hole transport layer in polymer solar cells

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