| 1. |
- Braun, Slawomir, 1977-, et al.
(author)
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Influence of the electrode work function on the energy level alignment at organic-organic interfaces
- 2007
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:20
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Journal article (peer-reviewed)abstract
- The energy level alignment at interfaces, in stacks comprising of (4, 4′ -N, N′ -dicarbazolyl-biphenyl) (CBP), (4,4, 4″ -tris[3-methyl-phenyl(phenyl)amino]-triphenylamine) (m -MTDATA), and a conductive substrate, has been studied. We show that the alignment of energy levels depends on the equilibration of the chemical potential throughout the layer stack, while any electronic coupling between the individual layers is of lesser importance. This behavior is expected to occur for a broad class of weakly interacting interfaces and can have profound consequences for the design of organic electronic devices. © 2007 American Institute of Physics.
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| 2. |
- Braun, Slawomir, 1977-
(author)
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Studies of Materials and Interfaces for Organic Electronics
- 2007
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Doctoral thesis (other academic/artistic)abstract
- Organic electronics is a rapidly evolving field with vast number of applications having high potential for commercial success. Although a great progress has been made, many organic electronic applications: organic light-emitting diodes (OLEDs), organic fieldeffect transistors (OFETs), organic solar cells, etc; still require further optimization to fulfill the requirements for successful commercialization. For many applications, available at this time organic materials do not provide satisfactory performance and stability, which hinders the possibility of a large-scale production. Therefore, the key ingredient needed for a successful improvement in performance and stability of organic electronic devices is in-depth knowledge of physical and chemical properties of molecular and polymeric materials. Since many applications encompass several thin film layers made of organics, and often also inorganic materials, the understanding of both organic-organic and hybrid interfaces is yet another important issue necessary for the successful development of organic electronics.The research presented in this thesis is based mainly on photoelectron spectroscopy, which is an experimental technique especially suited to study both surfaces and interfaces of materials. In the thesis, the properties of one of the most successful polymeric materials, poly(3,4-ethylenedioxythiophene), often abbreviated as PEDOT, have been extensively studied. The research was done in close cooperation with an industrial partner – AGFA Gevaert, Belgium. The study was focused on the exploration of the intrinsic properties of the material, such as stability, morphology and conductivity. In addition, however, a possibility of alternation of these properties was also explored. This thesis reports also about investigations of the properties of various organic-organic and hybrid interfaces. The energy level alignment at such interfaces plays important role in charge injection and performance of the thin film organic-based devices. The conditions for different energy level alignment regimes at the various interfaces have been studied. The studies on interfaces were performed in close collaboration with the R&D division of DuPont Corporation, USA. This work led to the significant advances in understanding of the interface energetics and properties of industryrelevant organic materials, as represented not only by published scientific papers, but also patent applications.
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| 3. |
- Osikowicz, Wojciech, 1974-, et al.
(author)
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Energetics at Au top and bottom contacts on conjugated polymers
- 2006
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 88:19
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Journal article (peer-reviewed)abstract
- Photoelectron spectroscopy was employed to examine the energetics, and therefore charge injection barriers, at top and bottom contact configurations of gold and conjugated polymers, i.e., polymer spin coated on gold and vapor-deposited gold on polymer interfaces. Very similar results are obtained for both ex situ (contaminated) and in situ (clean) prepared interfaces: a 0.7-0.8 eV decrease in the vacuum energy levels is consistently observed as compared to bare polycrystalline gold. These observations are explained by changes of the metal work function upon contacting either polymers or contaminants, associated with the reduction of the electron density tail that extends outside the metal surface. © 2006 American Institute of Physics.
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| 4. |
- Tengstedt, Carl, 1974-, et al.
(author)
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Ultraviolet light-ozone treatment of poly(3,4-ethylenedioxy-thiophene)-based materials resulting in increased work functions
- 2006
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In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:4, s. 2085-2090
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Journal article (peer-reviewed)abstract
- We describe a simple method to increase the work function of poly(3,4-ethylenedioxy-thiophene)-poly(perfluoroethylene sulfonic acid), PEDOT-PFESA, and poly(3,4-ethylenedioxy-thiophene)-poly(styrene sulfonic acid), PEDOT-PSS, by short exposure to ultraviolet light and ozone. The creation of carbonyl groups in the surface region forms a dipole layer shifting the vacuum level with a followed increase in work function. It has been shown that the work function of PEDOT-PFESA can be increased by as much as ∼ 0.4 eV to the absolute value of 6.3 eV and by at least ∼ 0.2 eV for PEDOT-PSS to the absolute value of 5.4 eV. The increase in work function has also proven to be time dependent with the largest increasing rate occurring for short exposure times. Upon ozone treatment, both PEDOT and PSS are oxidized whereas PFESA seems to be unaffected.
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| 5. |
- Wang, Ying, et al.
(author)
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Enhancement of iridium-based organic light-emitting diodes by spatial doping of the hole transport layer
- 2005
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87:19, s. 193501-
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Journal article (peer-reviewed)abstract
- The electroluminescence efficiency of Ir-based green emitter devices is very sensitive to the nature of the hole transport layer used. We show that by inserting a 1 nm layer of bis[4-(N,N-diethylamino)-2-methylphenyl](4- methylphenyl)methane (MPMP) in a 4, 4′ - bis- (carbazol-9-yl) biphenyl (CBP) hole transport layer, a device that combines the positive attributes of both MPMP (high efficiency) and CBP (low injection voltage) is obtained. These results can be understood based on a combined ultraviolet photoemission spectroscopy/inverse photoemission spectroscopy study, which reveals the very low electron affinity and superior electron blocking capability of MPMP. © 2005 American Institute of Physics.
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