liu.seSearch for publications in DiVA
Change search
Link to record
Permanent link

Direct link
BETA
Jönsson, Stina
Publications (10 of 13) Show all publications
Johansson, E., Sandell, A., Siegbahn, H., Rensmo, H., Mahrov, B., Boschloo, G., . . . Fahlman, M. (2005). Interfacial properties of photovoltaic TiO2/dye/PEDOT–PSS heterojunctions. Synthetic metals, 149(2-3), 157-167
Open this publication in new window or tab >>Interfacial properties of photovoltaic TiO2/dye/PEDOT–PSS heterojunctions
Show others...
2005 (English)In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 149, no 2-3, p. 157-167Article in journal (Refereed) Published
Abstract [en]

Systems comprising a dense TiO2 film electrode, a ruthenium polypyridine dye and a PEDOT–PSS (poly(3,4-ethylenedioxythiophene)–poly(4-styrenesulphonate)) film were prepared. The heterojunctions were shown to have photovoltaic properties, with the dye absorbing the light, the TiO2 acting as an electron conducting material and PEDOT–PSS acting as a hole transport material. A series of dyes was used to investigate their influence on the photocurrent and the photovoltage characteristics of the heterojunction. These results were compared to a photoelectrochemical system in which the PEDOT–PSS was replaced by a liquid electrolyte containing triiodide/iodide redox-couple.

Photoelectron spectroscopy (PES) was used to monitor the interfacial properties of the heterojunction and the investigation points out effects of importance when assembling the materials together to a functional unit. Specifically, it was concluded that the interaction with the dye clearly affects the structure of PEDOT–PSS, both with respect to the surface composition of PSS relative to PEDOT and with respect to the chemical state of the sulphur in the polymers. Moreover, a comparison of the Ru3d and the valence band spectra of the two different interfaces (dye/TiO2 and dye/PEDOT–PSS) indicates that the energy level structure of the dyes compared to the substrate is different for the two surfaces. Thus, in the combined energy level picture under dark conditions, the energy levels in TiO2 relative to the energy levels in PEDOT–PSS depend on the dye.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-32271 (URN)10.1016/j.synthmet.2004.12.004 (DOI)18159 (Local ID)18159 (Archive number)18159 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
de Jong, M. P., Friedlein, R., Sorensen, S. L., Öhrwall, G., Osikowicz, W., Tengstedt, C., . . . Salaneck, W. R. (2005). Orbital-specific dynamic charge transfer from Fe(II)-tetraphenylporphyrin molecules to molybdenum disulfide substrates. Physical Review B. Condensed Matter and Materials Physics, 72(3), 35448
Open this publication in new window or tab >>Orbital-specific dynamic charge transfer from Fe(II)-tetraphenylporphyrin molecules to molybdenum disulfide substrates
Show others...
2005 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 3, p. 35448-Article in journal (Refereed) Published
Abstract [en]

Orbital-specific femtosecond charge transfer dynamics between Fe(II)-tetraphenylporphyrin molecules and semimetallic molybdenum disulfide substrates is investigated using core-level resonant photoemission spectroscopy. The electronic coupling to the substrate and the efficiency of charge transport across the interface is found to be different for the individual molecular electronic subsystems. In particular, electrons excited at the phenyl substituents are transferred within 3–6 fs, while hopping from the porphyrin ring is slower than 30 fs.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-30230 (URN)10.1103/PhysRevB.72.035448 (DOI)15734 (Local ID)15734 (Archive number)15734 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
Jönsson, S., Carlegrim, E., Zhang, F., Salaneck, W. R. & Fahlman, M. (2005). Photoelectron spectroscopy of the contact between the cathode and the active layers in plastic solar cells: the role of LiF. Japanese Journal of Applied Physics, 44(6A), 3695-3701
Open this publication in new window or tab >>Photoelectron spectroscopy of the contact between the cathode and the active layers in plastic solar cells: the role of LiF
Show others...
2005 (English)In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 44, no 6A, p. 3695-3701Article in journal (Refereed) Published
Abstract [en]

The surfaces and electrode interfaces of a polymer blend used in prototype solar cells have been characterized with photoelectron spectroscopy. The polymer blend in question is a 1:4 mixture of APFO-3:PCBM. Based on surface analysis of the pristine film we can conclude that the surface of the blend is a 1:1 mixture of APFO-3 and PCBM. The electrode systems studied are the widely used Al and Al/LiF contacts. LiF prevents formation at the Al/organic interface of Al-organic complexes that destroy the π-conjugation. In addition to this, there are two other beneficial, thickness dependent, effects. Decomposition of LiF occurs for thin enough layers in which the LiF species are in contact with both the organic film and the Al atoms, which creates a low workfunction contact. For thicker (multi)layers, the dipole formed at the LiF/organic interface is retained as no decomposition of the LiF occurs upon Al deposition.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-30346 (URN)10.1143/JJAP.44.3695 (DOI)15883 (Local ID)15883 (Archive number)15883 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
Jönsson, S., Salaneck, W. R. & Fahlman, M. (2005). Photoemission of Alq3 and C60 films on Al and LiF/Al substrates. Journal of Applied Physics, 98(1), 14901-14907
Open this publication in new window or tab >>Photoemission of Alq3 and C60 films on Al and LiF/Al substrates
2005 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 98, no 1, p. 14901-14907Article in journal (Refereed) Published
Abstract [en]

Photoemission studies of thin films of Alq3 and C60 deposited on Al and LiF/Al substrates have been performed in order to deduce the interactions of the organic films with the substrates. For all cases there is evidence of strong interaction resulting in the formation of interfacial dipoles. Attempts to explain the origin of these interfacial dipoles and the type of interface formed in each case have been done through analysis of the valence electronic structure and core levels of the materials. The origin of the interfacial dipoles is mainly covalent interaction when the organic films are deposited on Al substrates, and charge transfer between the organic molecules and the metal through the LiF sandwich layer when the organic films are deposited on LiF/Al substrates. For thick-enough LiF films, however, there is no interaction between the organic films and the substrates. In no case does the LiF dissociate, unlike what is found for the reverse order of deposition. Two charge-transfer-induced gap states are found for (sub)monolayer films of Alq3 deposited on LiF/Al. We propose that the formation of two gap states corresponds to negatively charged fac-Alq3.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-32253 (URN)10.1063/1.1929884 (DOI)18133 (Local ID)18133 (Archive number)18133 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
Chen, M., Perzon, E., Andersson, M. R., Marcinkevicius, S., Jönsson, S., Fahlman, M. & Berggren, M. (2004). 1 micron wavelength photo- and electroluminescence from a conjugated polymer. Applied Physics Letters, 84(18), 3570-3572
Open this publication in new window or tab >>1 micron wavelength photo- and electroluminescence from a conjugated polymer
Show others...
2004 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 84, no 18, p. 3570-3572Article in journal (Refereed) Published
Abstract [en]

We report photo- and electroluminescence from an alternating conjugated polymer consisting of fluorene units and low-band gap donor-acceptor-donor (D–A–D) units. The D–A–D segment includes two electron-donating thiophene rings combined with a thiadiazolo-quinoxaline unit, which is electron withdrawing to its nature. The resulting polymer is conjugated and has a band gap of 1.27 eV. The corresponding electro- and photoluminescence spectra both peak at approximately 1 μm. Light-emitting diodes, based on a single layer of the polymer, demonstrated external quantum efficiencies from 0.03% to 0.05%.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-22529 (URN)10.1063/1.1737064 (DOI)1790 (Local ID)1790 (Archive number)1790 (OAI)
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13
Chen, M., Perzon, E., Robinson, N. D., Jönsson, S., Andersson, M., Fahlman, M. & Berggren, M. (2004). Low band gap donor–acceptor–donor polymers for infra-red electroluminescence and transistors. Synthetic metals, 146(3), 233-236
Open this publication in new window or tab >>Low band gap donor–acceptor–donor polymers for infra-red electroluminescence and transistors
Show others...
2004 (English)In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 146, no 3, p. 233-236Article in journal (Refereed) Published
Abstract [en]

We report on transistors and light-emitting diodes using a conjugated polymer consisting of alternated segments of fluorene units and low-band gap donor–acceptor–donor (D–A–D) units. The D–A–D segment includes two electron-donating thiophene rings combined with a thiadiazolo-quinoxaline unit, which is electron withdrawing to its nature. The resulting polymer is conjugated and has a band gap of around 1.27 eV. Here we present the corresponding electro- and photoluminescence spectra, which both peak at approximately 1 μm. Single layer light-emitting diodes demonstrated external quantum efficiencies from 0.03% to 0.05%. The polymer was employed as active material in thin film transistors, a field-effect mobility of 3 × 10−3 cm2/V s and current on/off ratio of 104 were achieved at ambient atmosphere.

Keywords
polymers, infra-red electroluminescence, band gap
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46161 (URN)10.1016/j.synthmet.2004.08.002 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Jönsson, S., Salaneck, W. R. & Fahlman, M. (2004). Spectroscopy of ethylenedioxythiophene-derived systems: from gas phase to surfaces and interfaces found in organic electronics. Journal of Electron Spectroscopy and Related Phenomena, 137-140, 805-809
Open this publication in new window or tab >>Spectroscopy of ethylenedioxythiophene-derived systems: from gas phase to surfaces and interfaces found in organic electronics
2004 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 137-140, p. 805-809Article in journal (Refereed) Published
Abstract [en]

Two relevant topics within the field of organic electronics have been studied with photoelectron spectroscopy. The organic material used is the successful polymer blend PEDOT-PSS. The first issue relates to the conductivity of organic materials. A known procedure (specific solvent-mixture) for improving the conductivity of PEDOT-PSS has been studied. The mechanisms behind the enhanced conductivity were shown to be due to higher PEDOT content at the surface. The other issue has to do with metal contacting of organic materials. Aluminum/PEDOT-PSS interfaces were studied. The formation of interfacial species was deduced with the aid of model molecules. We can conclude that it is mainly the PSS part that reacts with aluminum. Due to different surfaces in standard PEDOT-PSS and solvent-treated PEDOT-PSS, different interfaces are formed in the two cases.

Keywords
organic electronics, PEDOT-PSS, conductivity, interfaces, XPS, photon energy dependent depth profiling
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46219 (URN)10.1016/j.elspec.2004.02.120 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Jönsson, S. (2004). Towards flexible organic electronics: photoelectron spectroscopy of surfaces and interfaces. (Doctoral dissertation). Linköping: Linköpings universitet
Open this publication in new window or tab >>Towards flexible organic electronics: photoelectron spectroscopy of surfaces and interfaces
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Intensive studies of conjugated molecules and polymers are carried out all over the world with the intent of obtaining cheap and efficient organic electronic devices. The most mature application at the moment is the light-emitting diode, but also photovoltaic cells and different types of transistors shows promising results. Interest in these materials is based on possibilities of 'simple' and cheap processing techniques, comparing to inorganic compounds, in the manufacturing of devices. The understanding of the electronic and chemical structure of the surfaces and interfaces of these materials is a basic requirement for understanding the characteristics of the potential devices. Understanding the electronic structure of the pristine materials enables conclusions to be drawn concerning electrical and optical properties in these materials. The behaviour of the interface between metals and conjugated materials is one of the primary factors determining the suitability of using certain electrode/organic material combinations in device applications.

With this motivation, the electronic structure of both conjugated molecules and polymers surfaces and their interfaces to metals (and insulators) have been studied with mainly photoelectron spectroscopy (PES). In some cases complementary techniques have been needed and performed. This includes the four-point probe technique for determining surface resistance and atomic force morphology for determining surface morphology. As well as synchrotron-based techniques, such as near-edge X-ray absorption spectroscopy and resonant photoemission have been used. The main results compromised in this thesis are summarized below.

Poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid (PEDOT-PSS) is an aqueous colloidal dispersion consisting of doped conjugated polymer PEDOT with counter ions provided by the PSS chains. PEDOT-PSS films have previously proven to have a grain-like structure in which the grains have a ~30 Å thick insulating PSS outermost layer. The conductivity of thin PEDOT-PSS films has been improved through adding some high-boiling-point solvents to the PEDOT-PSS blend. The major reason for this increase is a rearrangement of the morphology, in terms of an increase in the PEDOT-to-PSS ratio in the surface region (i.e. the insulating PPS layer is decreased for each grain).

The initial stages of interface of PEDOT-PSS with aluminum for contacting purposes has also been examined. Due to the many components in the PEDOT-PSS film its reactions with alurninum was difficult to deduce. Therefore the aluminum interfaces with model molecules of each of the components of PEDOT-PSS were investigated to discern this. Phenyl-capped EDOT-trimer was used as a model oligomer for neutral PEDOT. It has been shown that aluminum preferentially interacts and forms covalent bonds with C-S carbons that causes a rearrangement of the charge density within the oligomer and breaks then-conjugation. In PEDOT-PSS blends the PEDOT part is left intact and alurninurn preferentially reacts with the SO3-H+ and/or SO3- species of the PSS part.

A specific blend of conjugated materials used in photovoltaic cells is a one to four mixture of APFO-3 (a low band gap copolymer based on alternating fluorene and donor-acceptor-donor units) to PCBM (soluble C60 derivative). The electrode systems studied are the widely used Al and Al/LiF contacts. We demonstrate a thickness dependent effect of the LiF layer in the Al/LiF/organic structure. LiF has a protective effect for all thickness preventing formation at the Al/organic interface of Al-organic complexes that destroy the Π-conjugation. In addition to this, there are two other beneficial effects (depending on LiF thickness). Decomposition of LiF occurs for thin enough layers in which the LiF species are in contact with both the organic film and the A1 atoms. This results in Li-doping of the organic films and creates a low workfunction contact. For thicker (multi)layers, the dipole formed at the LiP/organic interface is retained as no decomposition of the LiF occurs upon Al deposition.

We have shown the occurrence of interfacial dipoles at C60/LiF/Al interfaces and confirmed interfacial dipoles at Alq3/Al, C60/Al and Alq3/LiF/Al interfaces through vacuum level shifts. There is strong interaction with the substrates in all cases. There is evidence of covalent interaction between both Alq3 and C60 films with the AI substrates. The added LiF layer (between AI substrate and the organic film) prevents the covalent bonds from forming and the LiF does not dissociate in any case, unlike what is found in literature for the reverse order of deposition. For both Alq3 and C60 there is charge transfer from the Al substrate to the organic film through the LiF layer. However, if the thickness of the LiF layer exceeds 25 Å this charge transfer is blocked. The evolution of the electronic structure upon n-doping of the first Alq3 monolayer observed here is different from previous studies of n-doping mer-Alq3, indicating that there is preferential deposition and/or formation of the unusual facial isomer of Alq3 on the LiF/Al substrate. Our results are the first reported photoemission spectra of this isomer and its n-doped state.

The electronic structure of two new low band gap polymers (APFO-3 and APFO-7) based on donor-acceptor-donor groups copolymerized with fluorine units has been characterized. The valence band of APFO-3 seems to be highly dispersed and derived from orbitals delocalized over the whole polymer chain, where as the conduction band is nearly flat as it is derived from orbitals localized on the acceptor units. The existence of a dispersed valence band would predict good hole transporting properties, where as a flat conduction band would be expected to produce poor electron transporting properties. The electronic structure of APFO-7 has similarities to APFO-7 but it is also less clear. The larger size of the acceptor unit seem to distort both the valence band and conduction band shape as compared to APFO-3, however, so further work is needed to understand the more complex APFO-7 system.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2004. p. 56
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 895
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-22734 (URN)2039 (Local ID)91-85295-34-5 (ISBN)2039 (Archive number)2039 (OAI)
Public defence
2004-10-01, K3, Kåkenhus, Campus Norrköping, Norrköping, 10:15 (Swedish)
Opponent
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-01-29
Friedlein, R., Crispin, X., Simpson, C. D., Watson, M. D., Jackel, F., Osikowicz, W., . . . Salaneck, W. R. (2003). Electronic structure of highly ordered films of self-assembled graphitic nanocolumns. Physical Review B. Condensed Matter and Materials Physics, 68(19), 195414
Open this publication in new window or tab >>Electronic structure of highly ordered films of self-assembled graphitic nanocolumns
Show others...
2003 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, no 19, p. 195414-Article in journal (Refereed) Published
Abstract [en]

Highly ordered, several nanometers thick films of alkylated large planar, polycyclic aromatic hydrocarbon (PAH) molecules have been grown on semi-metallic molybdenum disulfide substrates. The films are characterized by a two-dimensional lateral arrangement of columns standing at the surface on a macroscopic scale. The self-assembly of such insulated columns of face-to-face disks with surface-induced vertical alignment has been achieved directly from solution processing. Angle-resolved photoelectron spectra revealed a highly anisotropic quasi-one-dimensional electronic structure with an extended π-electronic wave function. An intermolecular dispersion of the highest occupied band of at least 0.15 eV along the stacking direction has been measured. A partial breakdown of the concept of quasimomentum due to the finite size of the nano-objects perpendicular to the stacks is observed.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47736 (URN)10.1103/PhysRevB.68.195414 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Jönsson, S., de Jong, M. P., Groenendaal, L., Salaneck, W. R. & Fahlman, M. (2003). Phenyl-capped EDOT trimer: its chemical and electronic structure and its interface with aluminum. Journal of Physical Chemistry B, 107(39), 10793-10800
Open this publication in new window or tab >>Phenyl-capped EDOT trimer: its chemical and electronic structure and its interface with aluminum
Show others...
2003 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 107, no 39, p. 10793-10800Article in journal (Refereed) Published
Abstract [en]

The chemical and electronic properties of a phenyl-capped 3,4-(ethylenedioxy)thiophene trimer (EDOT trimer) and its interface formation with aluminum have been studied. Thin EDOT trimer films were prepared on clean gold substrates through in-situ vapor deposition. Aluminum was deposited stepwise on top of the EDOT trimer, and the initial stages of interface formation were investigated by photoelectron spectroscopy. The organic/metal interface formed was not completely abrupt; some degree of diffusion of aluminum into the EDOT trimer film occurred. The aluminum atoms preferentially react with the α-position of the trimer (C−S carbon atoms) forming covalent bonds. The formation of these covalent bonds causes a break in the π-conjugation of the system due to the introduction of sp3 defects. The charge density also is somewhat redistributed within the oligomer as a whole, mainly affecting the neighboring atoms:  sulfur and β-position of the trimer (C=C−O carbon atoms). Once the C−S carbon sites are saturated, the aluminum instead reacts with the less favorable carbon atom of the ethylene bridge (C−O−C carbons). Worth noting is the decrease in work function from 5.2 eV for sputter cleaned gold to 4.1 eV upon deposition of the EDOT trimer. Our results have several implications for organic electronics. The sp3 defects introduced by the aluminum−EDOT contacting will influence the charge injection into the material across the EDOT trimer/aluminum interface negatively. The change in work function could potentially be used to modify gold contacts for electron injection into molecules with low electron affinity.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47757 (URN)10.1021/jp034249p (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Organisations

Search in DiVA

Show all publications