Phone : +49 8928912452
- Current research
- Polymers for Application in Photovoltaics
- Selected Publications
- Nanostructured Polymer Films
- Advanced Scattering Techniques
- Functional Polymer Materials
- since 3/2015 member of "Advanced Light Source (ALS) Review Panel"
- since 9/2014 member of "Heinz-Maier-Leibnitz-Zentrum (MLZ) Review Panel"
- from 1/2012 and until 6/2015 Member of "Peer Review Panel 3 - Surfaces & Interfaces"' of "Diamond Light Source Ltd"
- since 9/2012 Associate Editor of journal ACS Applied Materials & Interfaces of the American Chemical Society
- since 3/2012 Head of keylab “TUM.solar” in the Bavarian Collaborative Research Project “Solar Technologies Go Hybrid” (SolTech)
- since 1/2012: Member of the Scientific Selection Panel of the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB)
- since 2011: German representative at European Polymer Federation (EPF) for polymer physics
- since 2011: elected member of the 9. Komitee Forschung mit Synchrotronstrahlung (KFS)
- since 2010: Managing Director of "Network Renewable Energies (NRG)" at Munich School of Engineering (MSE) of TU München
- since 2010: spokesman of Physik-Department at TU München in the field of energies
We investigate the physical principles of material properties of soft matter. General aim of our work in the field of nanostructured polymer interfaces is to deduce the functional properties of materials from the knowledge of the structure and dynamics in the nanoscale.
Polymers for Application in Photovoltaics
One potential alternative to crystalline silicon photovoltaic (PV) cells is cells made from thin films (<1 micometer) of conjugated (semiconducting) and photoactive polymers, which can easily be cast onto flexible substrates over a large area using wet-processing techniques. These photoactive polymers are attractive semiconductors for photovoltaic cells because they are strong absorbers and can be deposited on flexible substrates at low cost. Cells made with a single polymer and two electrodes (see figure 1a) tend to be inefficient because the photogenerated excitons are usually not split by the built-in electric field, which arises from differences in the electrode work functions. The efficiency can be increased by splitting the excitons at an interface between two semiconductors with offset energy levels (see figure 1b). The exciton diffusion length in several different conjugated polymers has subsequently been measured to be 4-20 nm. To address the problem of limited exciton diffusion length in conjugated polymers, two conjugated polymers with offset energy levels are mixed so that all excitons would be formed near an interface, as depicted in figure 1c [Appl. Phys. 1995, 78, 4510]. This device structure, called a bulk heterojunction (BHJ), provided a route by which nearly all photogenerated excitons in the film could be split into free carriers. To allow the transport of the free carriers to the electrodes a bi-continuous blend structure is most advantageous. The active layer, consisting of two interpenetrating sub-networks with donor, respectively acceptor character, is sandwiched between two charge carrier-selective contacts [Chem. Mater. 2004, 16, 4533-4542].
- G.Kaune, P.Müller-Buschbaum
phys.stat.sol. (RRL) 4, 52-54 (2010)
- G.Kaune, M.Memesa, R.Meier, M.A.Ruderer, A.Diethert, S.V.Roth, M.D'Acunzi, J.S.Gutmann, P.Müller-Buschbaum
ACS Appl. Mater. Interfaces 1, 2862-2869 (2009)
J.Phys.Condens.Matter 15, R1549 (2003)
- P.Müller-Buschbaum, E.Bauer, E.Maurer, K.Schlögl, S.V.Roth, R.Gehrke
Appl.Phys.Lett. 88, 083114 (2006)
- J-.F.Moulin, S.V.Roth, P.Müller-Buschbaum
Rev.Sci.Instr. 79, 015109 (2008)
- M.M. Abul Kashem, J.Perlich, A.Diethert, W.Wang, M.Memesa, J.S. Gutmann, E.Majkova, I.Capek, S.V.Roth, W.Petry, P.Müller-Buschbaum
Macromolecules 42, 6202-6208 (2009)
- P.Müller-Buschbaum, E. Bauer, E.Maurer, K.Schlögl, S.V.Roth, R.Gehrke
Appl.Phys.Lett. 88, 083114 (2006)
- P.Müller-Buschbaum, E.Maurer, E.Bauer, R.Cubitt
Langmuir 22, 9295 (2006)
Nanostructured Polymer Films
Nanostructured polymer surfaces are of strong interest with respect to basic research as well as for future applications. With the increasing demand on miniaturization of electronic devices the evolved polymer structures have to be decreased in their spatial dimensions as well. Due to the natural size of polymers, e.g. given by the radius of gyration of the unperturbed polymer chain, which is on the order of 10 nm, a simple scaling down assumption is limited. With structural sizes approaching the nanoscopic range significant changes in the underlying physical process occur. Examples are the slowing down of chain diffusion near surfaces, the modification of the chain conformation in ultra thin films and the shift in the glass transition temperature in thin films. In addition, the stability of these films is changed and a destabilization by dewetting will give rise to destruction of an initially homogeneous film. On the other hand this dewetting process can be utilized for the creation of nanostructured polymer surfaces. It is the aim to build-up controlled internal strcutures of periodically arrange diblock copolymer molecules which are confined into super-structures like droplets (originated from a second process, e.g. dewetting) acting as a matrix.
Advanced Scattering Techniques
To detect a lateral surface or interface roughness, lateral correlations, sizes and shapes of objects such as particles positioned on top of the surface or in an surface near region off-specular scattering is required. Usually information about in-plane structures are investigated with conventional diffuse (or off-specular) X-ray scattering. Due to a relaxed resolution in one of the three components of the scattering wave vector, these experiments are possible in laboratory based experimental set-ups. Compared to reflectivity measurements the demand for a high primary intensity is increased al-ready. As a consequence of the quite complex data fitting procedure required to extract the desired information from conventional diffuse scattering data, grazing incidence small angle scattering (GISAS) experiments receive an increasing attention within the last years. In case of many sample systems GISAS enables an easy access to the desired structural information, because the Fresnel transmission functions enter only as scaling factors. GISAS involves a combination of two techniques, GID (grazing incidence diffraction), which uses a reflection geometry to obtain surface and near surface sensitive scattering, and SAS (small angle scattering), which measures structures of 1 - 100 nm length in normal transmission mode. It is a non-destructive structural probe and does not require a special sample preparation. GISAS yields an excellent sampling statistics (averages over macroscopic regions to provide information on nanometer scale) and provides information on particle geometry, size distributions and spatial correlations. In GISAS experiments however, the high demand on collimation makes the use of high flux sources of large scale facilities such as synchrotron radiation advantageous. In addition, experiments were successfully per-formed with neutrons at high flux neutron reactors. Thus comparable to reflectivity measurements and conventional diffuse scattering, two probes namely X-rays and neutrons are available. Recently, micro-beam GISAXS experiments enabling a local resolution become possible picture the ongoing experimental developments in the field of GISAS.
Functional Polymer Materials
Nanocomposite materials based on a polymer matrix and inorganic nanoparticles fillers are of great importance in research because the desired physical properties can be rendered to the final product. Target properties are largely dependent on the arrangement of nanoparticles in the host matrix used. For special application purpose an ordered arrangement of the nanoparticles is desired. An ordered arrangement of nanoparticles can be achieved by using the template offered by self organization of block copolymers. The idea is to incorporate nanoparticles into spherical, lamellar or cylindrical microdomains formed by micro-phase separation of the block copolymer, which can be done for example, either by removing one block and using as a mask for plating or by etching through the film and transferring the pattern to a solid substrate. Another method is to tailor the surface of nanoparticles in a way that the block copolymer self-assembles with the nanoparticles that organize themselves selectively in one block.
schematic of combining block copolymer templated matrix and polymer coated nanoparticles