Research Topics

Dye-sensitized solar cells

Dye-sensitized solar cells

For regenerative energy sources, not only high efficiencies but also economical facts are important. Therefore, the well-developed high-efficiency solar cells are not competitive to traditional energy sources without financial support.
The development of dye-sensitized solar cells (DSSCs) represents a promising alternative to conventional Si-solar cells due to their good cost-to-performance-ratio. However, the efficiencies and lifetime are lower than Si solar cells up to now. In addition, the DSSCs could be an answer on the ERoEI problem of the conventional photovoltaics (invested energy return problem).
In our group we focus on fundamental aspects of charge transfer mechanisms in DSSCs which we consider as not fully understood ⁽¹⁾. Furthermore, we investigate effects and processes that are influencing the DSSCs lifetime.

⁽¹⁾ F. Marlow, A. Hullermann, L. Messmer: Is the Charge Transport in Dye-sensitized Solar Cells Really Understood? Adv. Mater. 27 (2015) 2447–2452
DOI:10.1002/adma.201404883.

 

Opals and photonic crystals

Opals and photonic crystals

Opals are not only beautiful gemstones, they also have fundamental significance as prototypes for photonic crystals. They may lead to new photonic and photocatalytic materials. The crucial problems of these materials are the spontaneous defects and the desired incorporation of specially designed defects. In the works below, we described basic ideas and our approaches to special topics.

Review:
F. Marlow, Muldarisnur, P. Sharifi, R. Brinkmann, C. Mendive:
Opals: Status and Prospects
Angew. Chem. Int. Ed. 2009, 48(34), 6212
DOI: 10.1002/anie.200900210

Fabrication of PhCs:
M. Muldarisnur, F. Marlow: Observation of Nano-Dewetting in Colloidal Crystal Drying. Angew. Chem. 53(33) (2014) 8761-8764
DOI: 10.1002/anie.201402423

F. Marlow, W. Dong:
Engineering Nanoarchitectures for Photonic Crystals.
ChemPhysChem. 4 (2003) 549
DOI: 10.1002/cphc.200200531

H. Li, F. Marlow:
Controlled Arrangement of Colloidal Crystal Strips.
Chem. Mater. 2005, 17, 3809
DOI:10.1021/cm051114i

Properties of Opals:
Muldarisnur and F. Marlow:
Crystal Orientation and Defects.
J. Phys. Chem. C 115 (2011) 414
DOI:10.1021/jp108975p

Fabrication of potential PhC Units:
Tian-Song Deng, P. Sharifi, F. Marlow:
Opal Shell Structures: Direct Assembly versus Inversion Approach
ChemPhysChem 2013, 14, 2893-2896
DOI: 10.1002/cphc.201300456
 

Low-n films and other optical materials

Low-n films and other optical materials

Mesoporous structures are more than just materials with pores (2 nm < d_meso < 50 nm) bigger than micropores (d_micro < 2 nm). They show new structures, shapes and symmetries that induce new properties and reveal unexpected applications. A central point of our research is one especially-perfect class of mesoporous structures (circulites), exhibiting circularly arranged pores which represent a novel symmetry behavior. These structures are strictly-defined hierarchies which can serve as a prototype for the description and formation of hierarchical structures. Here, coiling is regarded as a general approach to the assembly of hierarchies. The control and design of hierarchical structures are the ultimate aims and have been achieved for this hierarchy type. Surfaces can be used for the selection of the hierarchy type, position control and alignment of the resulting particles. A molecular structuring of the support leads to pixel-like, highly-defined growth of a hierarchical arrangement containing 4 hierarchy levels. The properties of the hierarchies can be very specific, as the diffusion behavior. Important achievements are described in the following papers:

M. Schmidt, G. Boettger, M. Eich, W. Morgenroth, U. Huebner, H. G. Meyer, D. Konjhodzic, H. Bretinger, F. Marlow:
Ultra low refractive index substrates – a novel base for photonic crystal slab waveguides.
Appl. Phys. Lett. 85 (2004) 16-18. Web-Reprint: Virtual Journal of Nanoscale Science & Technology, 10 (2004) Issue 2
DOI:10.1063/1.1767962

D. Konjhodzic, H. Bretinger, U. Wilczok, A. Dreier, A. Ladenburger, M. Schmidt, M. Eich, F. Marlow:
Low-n Mesoporous Silica Films: Structure and Properties.
Applied Physics A 81 (2005) 425
DOI:10.1007/s00339-005-3244-y

F. Marlow, M.D. McGehee, D. Zhao, B.F. Chmelka, G.D. Stucky:
Doped mesoporous silica fibers: A new laser material.
Adv. Mater. 11 (1999) 632.
DOI:10.1002/(SICI)1521-4095(199906)11:8<632::AID-ADMA632>3.0.CO;2-Q

J. Loerke, F. Marlow:
Laser Emission from Dye-Doped Mesoporous Silica Fibers.
Adv. Mater. 14 (2002) Issue 23
DOI: 10.1002/1521-4095(20021203)14:23<1745::AID-ADMA1745>3.0.CO;2-M
 
 

Nanoparticel aggregates

Nanoparticel aggregates

This research area was active in our research group until 2013, but it has still an influence on the on-going research.

Many synthesis techniques deliver interesting brick stones for nanotechnology, but how can we assemble them in a reasonable manner? Very likely, there is not a single universal procedure to construct nano devices. Such devices have to be generated by a whole hierarchy of assembly steps. The aggregation in emulsions is a promising tool on the lowest hierarchy level. NPAs are one possible step towards more complicating assemblies.

Publication:
D. Schunk, S. Hardt, H. Wiggers, F. Marlow:
Monodisperse titania microspheres via controlled nanoparticle aggregation.
Phys. Chem. Chem. Phys. 14 (2012) 7490-7496.
DOI: 10.1039/C2CP40658F

General Description:
D. Schunk, F. Marlow: NanoEnergie 7
(CENIDE Newsletter Juni 2012)

Solids with novel symmetry properties

Solids with novel symmetry properties

This research area was active in our research group until 2007, but it has still an influence on the on-going research.

A prerequisite for an efficient „molding the flow of light“ by photonic crystals is the molding of materials in desired nanostructures. Very often, conventional materials and processing techniques cannot fulfill the theoretical requirements for the materials and structures. Sol-gel methods enable material processing in opal pores and the controlled introduction of pores into materials. The porosity can be used for lowering the refractive index, for soft processing of the materials and for stress relaxation. Examples for this approach are ultra-low refractive index films used as supports for 2D photonic crystals, inverse opals with a skeleton-like unit cell filling and ferroelectric films with high transparency. Especially we are able to fabricate mesoporous silica films with a refractive index of 1.14 for use in 2D photonic crystal waveguide systems. Important achievements are described in the following papers:


Magdalena Stempniewicz, Ahmed S. G. Khalil, Michael Rohwerder, and Frank Marlow:
Diffusion in Coiled Pores - Learning from Microrelease and Microsurgery.
J. Am. Chem. Soc.129 (2007) 10561. 
DOI: 10.1021/ja0728167

F. Marlow, A. S. G. Khalil, M. Stempniewicz:
Circular mesostructures: Solids with novel symmetry properties. Invited Feature.
J. Mater. Chem. 17 (2007) 2168-2182
DOI: 10.1039/B700532F

A. S. G. Khalil, D. Konjhodzic, F. Marlow:
Hierarchy Selection, Position Control, and Orientation by Patterned Surfaces.
Adv. Mater. Vol 18, (2006) 1055.  
DOI: 10.1002/adma.200502238
 

Research Reports

• Research Report 2011 - 2013

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