Mechanical stability of organic solar cells
ved Michela Prete
Organic solar cells (OPVs) are considered, nowadays, a promising alternative to the inorganic PVs thanks to their low fabrication cost, the easy processability and tunability to different applications. In respect to the latest, organic materials allowed, in fact, the fabrication of flexible and stretchable devices opening the door to the possibility of mass production. These advantages are still limited by the ongoing improvement on the stability and efficiency of the organic devices. Although the efficiency has reached 12%, the final commercialization of the OPVs is still dependent on their stability. If different have been, in the past years, the photochemical stability studies, still few are the reported analysis on the mechanical properties of the organic devices. It is very important to understand the mechanical properties of the materials utilized, as much as understanding the results of the mechanical stress on flexible cells that is affecting the performances of the device over time. The main goal of the research project is to gain insight into the mechanical properties of flexible organic solar cells and to explore the possibilities of increasing the mechanical durability and stability of the cells while maintaining scalability and high electrical device performance. The project therefore encompasses work and specific objectives on determining the influences from both photochemical and mechanical stressing of flexible organic solar cells, and on applying specific additives that stabilize the cells against these degradation factors, both individually and combined. The work builds upon initial work on photochemical stabilization of organic solar cells, from where the initially tested photochemically stabilizing additives are chosen.
Vejledere: Morten Madsen og Vida Engmann
Hyperspectral thermal camera
Ved Anders Christian Løchte Jørgensen
This industrial PhD project is conducted in a collaboration between Newtec Engineering A/S and SDU. It focuses on the development of a hyperspectral thermal camera that can be used for thermography of buildings. Thermography of buildings is used to determine energy classification and find areas of poor thermal isolation. Present day thermal cameras only allow acquisition of greyscale images showing the intensity of infrared light in each pixel. This approach neglects the varying emissivity of materials which causes incorrect temperature measurements. In contrast, a hyperspectral camera measures the infrared light intensity at several wavelengths generating a full spectrum in each pixel in the ideal case. With this information, it will be possible to recognize a material through its emissivity, and thereby get a more accurate temperature determination. The project includes experimental work to develop and characterize the essential components for the camera. This includes the development of a graphene-based infrared sensor and of a multi-layered thin film mirror for a Fabry-Pérot interferometer used for spectral filtering. The sensitivity of the graphene sensor will be optimized by using quantum dots and plasmonics active in the infrared regime.
Vejleder: Jakob Kjelstrup-Hansen
Advanced Imaging of Biological Samples using Ion Beam Microscopy and Related Techniques
Ved Irina Iachina
A newly introduced high resolution method is Helium Ion microscopy (HIM). This technique is similar to scanning electron microscopy (SEM) but instead of electrons incident on a sample He ions are used. In HIM secondary electrons are usually imaged as in SEM. There are several advantages with HIM compared to SEM. Firstly, He ions have a smaller de Broglie wavelength than electrons which makes it possible to achieve a higher resolution than with SEM. The wavelength of Helium ions does not depend as strongly of the acceleration voltage making it possible to image high-resolution samples with lower voltages than the corresponding SEM. The decreased voltage reduces sample damage making it easier to achieve high resolution images of biological samples. However, the sample must still be dehydrated as the ion beam must be kept in vacuum. Not only is it possible to achieve higher resolution images of biological samples with lower voltages, it is also possible to image cross-sections of samples by the use of surface sputtering. Surface sputtering occurs when the kinetic energy from the incident Helium ions is transferred to the surface atoms. This energy transfer results in the surface atom being ejected (sputtered) from the lattice which makes it possible to etch away surface atoms from the sample and therefore image the different layers of a given sample.
The first part of the project is optimization of sample preparation and imaging of biological samples, such as human kidneys and human skin, with HIM. As HIM has the advantage of being able to image cross-sections by milling using surface sputtering, part of the project will include development of procedures for milling in human kidney samples, firstly by simulations of ion milling in biological samples and then by using HIM. Chemical contrast mechanism in HIM will also be investigated in order to distinguish between different chemical components in the biological samples. For this appropriate image analysis must be developed. The second part of the project will be the development of a method for correlative microscopy, firstly for HIM and confocal microscopy and then expanded to Optical Coherence Tomography (OCT), TiCo Raman, Scanning Electron Microscopy (SEM), confocal microscopy, Stimulated Emission Depletion (STED) microscopy and Coherent Anti-Stokes Raman Scattering (CARS) microscopy. The acquired methods can then be utilized to examine the same area with different microscopes. The last part of the project will include the development of an appropriate image analysis to enable the understanding and combination of the images acquired by correlative microscopy.
Vejleder: Jacek Fiutowski
Quantum Transport in Nanostructures
Ved Reza Abolhassani
Confronted with the desires of further technological developments, traditional devices based on silicon are reaching their upper limits, and new materials and nanotechnology are called to open a new era. Diamond is increasingly being recognized as a piece of jewelry for science and technology, due to a broad spectrum of its properties and wide-ranging applications. The extraordinarily high breakdown voltage and thermal conductivity, remarkable inertness to chemicals and contamination, and tunable electronic properties upon doping make diamond a promising material for unveiling new quantum physics and developing the next-generation electronics.The aim of this PhD project is to build the foundation for diamond-based nanoelectronics. The state-of-the-art nanofabrication techniques will be used to pattern lab-grown diamond thin films into certain nanostructures and devices. Then, the quantum electronic properties will be characterized by performing ultralow-noise electrical transport measurements under extreme conditions (at low temperatures and in high magnetic fields), alongside a range of standard thin film characterization techniques.
Vejleder: Horst-Günter Rubahn
X-ray and neutron scattering studies of metal oxide interlayers for photovoltaic applications
Ved Mariam Ahmad
Organic solar cells (OSCs) have gained a lot of popularity during the last 10 years since they are light weight, have a flexible structure and can be produced at low cost. These properties make OSCs promising candidates for cheap mass production as opposed to their commonly used inorganic counterparts. OSCs have not yet been industrially implemented for energy production due to challenges in obtaining high power conversion efficiencies but with the latest OSCs reaching efficiencies above 17 %, it is only a question of time before OSCs can be mass produced and implemented for cheap and sustainable energy production. One main challenge that the current OSCs are facing is obtaining long-term device stability. The current OSCs are prone to degradation over short time, which makes them ineligible for mass production in their current state. More research in device stability of OSCs is therefore needed before mass production can become a reality. The implementation of sputter deposited metal oxide interlayers such as MoOx and TiOx as charge-selective transport layers in OSCs has shown a higher long-term stability and an overall better device performance. These metal oxides will be the focus of this PhD project. The aim of the project is to develop sputtered MoOx and TiOx thin films for OSCs and study their detailed structure and properties using X-ray and neutron scattering at large-scale facilities. The degradation process will be studied upon subjecting the metal oxides to heat, light and oxygen and the electronic properties of the metal oxide interlayers will be studied using XPS and X-ray absorption. Device fabrication of OSCs containing the metal oxides will also be part of this project. The project is a part of the SMART (Structure of Materials in Real Time) lighthouse consortium.
This project is conducted in collaboration with Aarhus University, Prof. Bo Brummerstedt (Head of the UFM ’SMART’ ESS lighthouse) and Paris-Sorbonne University, Prof. Nadine Witkowski.
Vejleder: Morten Madsen
High-accuracy prediction of meat expiration dates by overcoming non-linearity barriers for microcantilever biosensors
Ved Lawrence Nsubuga
There is a yearly waste of 137,500 tons of meat and fish products in Denmark, of which about 43,000 tons are wasted due to overly careful expiration date estimations, resulting into high carbon emissions. Today households, restaurants, catering, and food stores rely on the printed expiration date, which is based on general prediction curves for meat degradation. For example, for pork cuts at 5°C under aerobic conditions the prediction curve says 8 days (+/-) 3 days. So, to be on the safe side, expiration dates are set to 5 days. The only means to control actual freshness of meat products are microbiological tests conducted at external laboratories requiring shipping of samples, growing, and counting bacteria. Such tests are seldomly carried out, since they are expensive (app. 335 € /sample), time consuming (48 hours) and do not predict the exact expiration date. There are other analysis methods available, but they all need to be carried out at external laboratories, e.g., measurement of cadaverine levels using gas chromatography mass spectrometry. Cadaverine is a volatile biogenic amine providing an exact measure for meat spoilage level. The amount of cadaverine gas increases in a predictable way over time depending on the type of meat. This PhD project proposes to realize great potential for CO2 reduction, by development of a biosensor for cadaverine in meat, enabling on-site highly accurate prediction of meat expiration dates. The main objective is to develop a biosensor enabling precise measurements of low levels of cadaverine and use this to predict meat expiration dates. Very small differences in cadaverine levels, at an early deterioration stage, translates into large differences with respect to expiration date. Therefore, it is a strict requirement that the biosensor enables high-accuracy measurements of +/- 10% at low levels of cadaverine, down to 10μg per kg of meat. To achieve this, we must overcome current state-of-the-art barriers; that microcantilevers provide nonlinear responses and that mathematical response processing models for nonlinearity compensation are lacking. The research hypothesis is that an array of microcantilever beams in different sizes or with different coatings, leading to different characteristic frequency modes, will enable dynamic real-time monitoring of an array of constants that can be fed into a mathematical model developed for non-linearity compensation.
Vejleder: Roana Melina de Oliveira Hansen