Synthesis and physical characterization of atomically thin FeS2

Background:

Thin-film solar cells, due to reduced materials cost and promising efficiency, gain momentum in large-scale deployment of photovoltaic technology for solar-to-electric power conversion with a potential to meet the grid parity with that of conventional fossil fuel based energy production. The champion materials for thin-film solar cells are crystalline silicon (c-Si), CdTe, and CuIn1-xGaxSe2 (CIGS). However, rareness and toxicity of Cd, Te, In and Se limit their widespread application. In pursuit of alternative materials, iron pyrite (FeS2) is an interesting alternative with comparable high absorption of CdTe and CIGS, and with high abundance, low-toxicity, as well as proven stability over geological time scales. United States geological survey studies has ranked FeS2 as the best among the 23 inorganic photovoltaic materials based on annual electricity production potential.

Despite these impressive properties and ranking, solar-to-electric power conversion efficiency of FeS2 is < 3% because of disappointingly low open circuit voltage (VOC < 0.2 V, ~ only 20 % of bandgap). If the efficiency can improve to 10%, the estimated production cost of electricity with FeS2 can fall as low as < 0.000002 ¢/W. Apparently, a 10% efficiency look far beyond the reality, however, it is argued that if the VOC can increase to 500 mV, we can reach a conversion efficiency of ~ 20%. Therefore, intensive research is needed to improve the VOC of FeS2 based solar cell.

In this regard, this project aims to synthesize ultrathin 2D FeS2, and characterize its photophysical properties for fundamental investigations and for future solar cell applications.

Project description:

Exfoliation, intercalation, and liquid metal reaction will be exercised to figure out a scalable synthesis route for atomically thin FeS2. State-of-the art characterization techniques will be employed to understand its (i) photophysical properties using UV-Vis spectroscopy, (ii) vibrational properties using confocal Raman Spectroscopy, (iii) morphology using TEM, SEM and AFM, (iv) chemical states using EDX, XPS, and FTIR.

The information obtained from this project will be used to engineering the pyrite phase of FeS2 for fabrication of high efficiency extremely thin film solar cells.

The proposed work will be performed at the division of Solid State Physics, Department of Engineering Sciences, Uppsala University. The suitable candidate should have, at least, basic knowledge on materials science, solid-state physics, and materials chemistry. Additionally, some knowledge in nanomaterials synthesis and understanding of physical characterization technique is a plus but not mandatory. Good knowledge of physics and/or chemistry is mandatory.

For question and enquiries, please contact: Dr Mohammad Ziaur Rahman (e-mail: mohammad.rahman@angstrom.uu.se; Phone# +46701679705)

Impedance spectroscopy measurements for the development of thinner and stronger glass

Background:

Glass as a material has the ability to contribute to the solution of several societal challenges that we are facing today. More glass than ever is used in buildings because of the transparency of glass, which lets sunlight into buildings and increases human well-being. Glass has also gained increased use through displays and solar energy, while glass packaging loses its market share to plastics, mainly because it is a heavier material. Glass is energy-intensive to manufacture and in order to manufacture thinner glass products, the glass needs to be made stronger. Chemical strengthening of glass is an old invention but has relatively recently achieved proper commercial success. However, the understanding of chemical strengthening is still not complete in several aspects, due to the complexity of the process and its mechanisms. Through a better understanding of the mechanisms, the possibilities of improving chemical strengthening of glass will be opened up.

Project Description:

The glass composition affects chemical strengthening a great deal since it is based on interdiffusion of larger ions from a molten salt bath into the glass and smaller ions out of the glass. Impedance spectroscopy is a method to measure the frequency-dependent electrical properties of a material. In the present project, it will give the opportunity to study the effect of the glass composition on the ionic conductivity, which is proportional to ion diffusion. The origin of the frequency dependence is one of the unresolved problems in physics and comparisons with different theoretical models are called for. In this project we wish to study the effect of titanium oxide on the electrical properties of glass and interpret the results using fundamental theoretical models. We will also correlate the ionic diffusion to structural data from vibrational spectroscopy measurements and basic physical-chemical knowledge.

The thesis will be jointly supervised by Uppsala University and RISE Glass, located in Växjö. The work will involve literature review, glass preparation and characterization of glasses. The majority of the work will be performed at the division of Solid State Physics, Department of Engineering Sciences, Uppsala University. RISE will provide glass samples to be measured at the Ångström Laboratory, Uppsala University. Good knowledge of physics and/or chemistry is mandatory.

If you are interested contact Prof. Gunnar Niklasson at the department of Solid State Physics or Stafan Karlsson at RISE Glass

Fabrication and evaluation of multilayered photocatalytic films

We advertise a master thesis work on solar light enhanced self-cleaning and air purifying coatings. The project will use a novel method to increase the photocatalytic reactivity of thin titanium dioxide (TiO2) films by means of a multilayer approach, whereby a thin TiO2 film is sputter deposited on a solar light absorbing substrate, either simulating a solar absorber or selective near infrared absorbing film. The main idea behind the project relies on harvesting absorbed solar heat and transport of this heat to a thin photocatalytic layer. This approach facilitates temperature dependent control of water coverage and reaction rates, which is expected to enhance the activity of the multilayer film. The project is of experimental nature and includes thin film techniques to make films, materials characterization (primarily XRD and spectrophotometry), optical modelling to obtain optimal thicknesses for the multilayer structure, and evaluation of the catalytic performance. The results will be analyzed by kinetic modelling and benchmarked against comparable films deposited on substrates that do not absorb infrared light.

If you are interested contact Lars Österlund or Andreas Mattsson