Functional Materials

Course with Participations of Group Members

Offers for Theses in the Group

High efficiency next generation organic solar cells

Next generation organic solar cells are solar cells beyond the silicon type photovoltaic devices. Organic solar cells have reached efficiencies in the champion solar cells well above 18%. Key element of such solar cells is the highly designed active layer, which transfers light into separated charge carriers. Aim of this experimental project is the preparation and full characterization of an active layer for high performance organic photovoltaic devices to further understand the fundamental correlation between morphology and solar cell performance. In this work a novel efficiency record-setting system will be investigated regarding the influence of an additional third component, in our case, either solvent additive or polymer. The project will involve a literature review, sample preparation, photovoltaic device fabrication and photoluminescent measurements. The focus is the usage of advanced scattering techniques for the determination of structural length scales of the active layer in the solar cell.

suitable as

• Master’s Thesis Applied and Engineering Physics

Supervisor: Peter Müller-Buschbaum

Lithium-ion batteries with modified electrolyte for next generation batteries

Lithium-ion batteries are an indispensable energy supply in modern society. The ideal anode consists of lithium metal due to its high specific energy and low electrochemical potential. However, lithium-ion batteries with liquid electrolyte are prone to form lithium dendrites, which can lead to failure or even explosion of the battery. Therefore, polymer electrolytes are an attractive alternative to bypass these obstacles. However, polymer electrolytes suffer from high contact resistances and low ionic conductivities, which requires an elevated operating temperature. In this project, a hybrid electrolyte based on liquid electrolyte modified with polymer will be prepared. Then, CR2032 coin cell batteries will be fabricated and tested with standard cycling procedures. Besides electrochemical characterization techniques, complementary measurement like real space imaging techniques (scanning electron microscopy, SEM) and reciprocal space techniques (small angle x-ray scattering, SAXS) can be performed. Overall, this master thesis project involves literature review, sample preparation and data analysis.

suitable as

• Master’s Thesis Applied and Engineering Physics

Supervisor: Peter Müller-Buschbaum

Low-temperature fabrication of titania films for hybrid solar cells on flexible substrates

Low-temperature (<150°C) route towards titania films offer promise for simple manufacturing, compatibility with flexible substrates, and titania-based solar cells. Herein, we use a specific titania precursor, ethylene glycol-modified titanate, to fabricate titania films as an electron-transporting layer. This experimental bachelor thesis aims at understanding the working principle of hybrid solar cells and the corresponding fabrication process. Different film characterization will be used such as SEM, GISAXS, XRD, UV-Vis, XPS, etc. The project will involve a literature review, sample preparation process, data analysis and result evaluation.

suitable as

• Master’s Thesis Applied and Engineering Physics

Supervisor: Peter Müller-Buschbaum

Printed perovskite solar cells

Organic-inorganic lead halide perovskite solar cells have recently achieved 25.5% efficiency owing to their tunable bandgap, high carrier mobility and long diffusion length. Nevertheless, most of the solar cells were fabricated based on the spin-coating method, which suffers from waste of material and missing scalability. In this regard, the printing technique, a simple and scalable method, is advantageous to realize a future commercial application of perovskite solar cells. In this project, we aim to fabricate perovskite solar cells by printing and have an overall understanding of the growth mechanism of the perovskite film during printing. We use imaging techniques (e.g. electron microscopy) and methods for structure and morphology determination, e.g. X-ray scattering.

suitable as

• Master’s Thesis Applied and Engineering Physics

Supervisor: Peter Müller-Buschbaum

Printed polymer-based thin film batteries

Materials for high energy density, solid-state batteries have been tremendously explored in the last decade. In particular, lithium-ion technology has attracted major interest. Among the many different types of batteries, the so-called polymer-based thin film batteries are very attractive as they can be incorporated into thin film devices. An inherent important part of such thin film lithium ion batteries is the membrane and solid-state polymer electrolyte membranes have attracted high attention in this respect. Lithium ions’ incorporation into solid-state polymer electrolyte membranes had shown a significant effect on both, the structure and properties, of the membranes in either the bulk or film format. The morphological reorganization and the thermodynamic properties of the solid-state polymer electrolyte membrane upon adding lithium salts and small molecules are the subjects of the experimental investigation. The polymer membranes will be prepared with printing. The structure and crystallinity of the lithium-doped membranes at different temperatures will be investigated with small/wide-angle X-ray scattering (SAXS/WAXS). The effects of morphology on the ionic conductivity of these ion-conducting membranes will be investigated using impedance spectroscopy. Aim of the present study is to increase conductivity with the help of small molecule additives, which can further improve the membrane morphology beyond the possibilities of the standard approach. Such high conductivity will be very beneficial for further downsizing of polymer-based thin film batteries.

suitable as

• Master’s Thesis Applied and Engineering Physics

Supervisor: Peter Müller-Buschbaum

Smart nano-sensors made of stimuli-responsive polymers in solution and in thin films

Whereas macroscopic sensors made of stimuli-responsive hydrogels are well established, in the nanoworld such sensors still face many challenges. Potential fields of application of such sensors extend from engineering to bioengineering and medicine, e.g. as nanosensors for the control of concentration of glucose for diabetes patients or as switchable surface in the frame of tissue engineering. In this experimental project smart hydrogels, made of stimuli-responsive hydrogels will be investigated. Hydrogel films with thicknesses of a few tens to some hundreds of nanometers and spontaneously deswell or swell due to external stimuli, like temperature or the concentrations of ions. The changes in thickness and in molecular interactions in swelling or collapsing hydrogels will be probed during the switching process by different lab-based techniques. A comprehensive understanding of the switching process can be achieved by complementary neutron scattering experiments at large scale facilities. The project will involve a literature review, preparation of hydrogels, as well as experimental investigations and interpretations of the repeated switching of the stimuli-responsive hydrogels.

suitable as

• Master’s Thesis Applied and Engineering Physics

Supervisor: Peter Müller-Buschbaum

Synthesis and self-assembly of gold nanoparticles for optoelectronic devices

Gold nanoparticles (Au NPs) show peculiar optical and electrical properties compared with the macroscopic metal owing to the characteristic of a nanoscale. Recently many advantages were made in optoelectronic devices applications with broadening band and energy transfer. In this project, your work will focus on the Au NPs structure regulation, since the size, density, and morphology of the Au NPs will influence the crystallinity of the photoactive film and charge transportation of the device. Specifically, you can work on one of the following topics: a) Synthesis and investigate optical properties of different morphology of gold nanoparticles b) Self-assembly of monolayer Au NPs array for optoelectronic devices.

suitable as

• Master’s Thesis Applied and Engineering Physics

Supervisor: Peter Müller-Buschbaum

Current and Finished Theses in the Group