Below is a list of topics we (soon will) work on. As we are in a build-up phase this list may not always be accurate. See also the publication list for an impression of our research interests.
Regarding methods, we are experimentalists. However, (predominantly numerical) modeling plays an important role in understanding experimental results and in designing novel devices.
Organic solar cells
The type of organic solar cells we work on consist of a mixture of two components, of which at least one is light-absorbing. Light absorption creates excitons that are split into an electron and hole at an interface between the two components. The electron accepting and donating components subsequently transport the electron and the hole to electrical contacts to which external circuitry can be connected.
Our interest is mainly in the fundamental processes involved in the generation of charge from excitons and the subsequent transport of these charges to the electrodes. Crucial factors are the energetic and structural disorder in the active material, which, both for better and worse, affect charge kinetics and energetics, i.e. the performance of the solar cell. Insight in such phenomena can for instance help to minimize voltage losses.
We have a special interest in solar cells that harvest in the long-wavelength regime; sub-visible radiation makes up about half of the solar energy. In conventional solar cells this energy is lost, but harvesting this IR radiation is not trivial and requires redesign of the solar cell.
On paper, ‘heat’ is an extremely abundant source of energy, being available as waste product and as part of the solar spectrum. Unfortunately most heat is of relatively low quality, i.e. the associated temperature differs only little from the ambient. Turning such low-quality heat into electricity in a cost-effective manner is not a trivial task.
Thermoelectric generators (TEG) turn heat (differences) into electrical power with reasonable efficiencies. However, most conventional (inorganic) TEG rely on rare elements and/or expensive nanostructuring. Disordered organic semiconductors have recently shown very promising thermoelectric behavior. How this behavior can be fundamentally understood is largely unknown. Even more importantly, for sure the performance limits of organic or other disordered material based TEG have not been reached. Fundamental understanding and improving performance by device and material design are our goals in this field.
The ratchet as a ‘scientific device’ was conceived about a century ago as a thought experiment to test the 2nd law of thermodynamics (‘no work can be extracted from a system in equilibrium’); the device on the top seems to defy the 2nd law. For our purposes a ratchet is loosely defined as a device where some sort of periodic but asymmetric potential is used to direct the otherwise random motion of particles when the system is driven away from equilibrium. Think of marbles running uphill on a shaking washboard (bottom).
Seen from a distance, a ratchet is a device that transforms one sort of energy (in the example shaking) into another (uphill motion). In our realm, we use the ratchet concept to convert (long wavelength) light and heat into electrical power. A great characteristic of ratchets is that many small contributions (uphill steps) are combined into something substantial. Ratchets also turn out to be intriguingly complex and counterintuitive devices.
Apart from being physically rich systems, ferroelectric materials are relevant for a wide variety of applications like data storage (e.g. FeRAM), actuation, transduction and energy harvesting. Traditionally, ferroelectric materials are inorganics. Our motivation to look into organic ferroelectrics is the possibility to change, improve and add functionality through modification of the molecular structure. For this we collaborate with organic chemists. The figure shows the well-known polymer ferroelectric p(VDF:TrFE) (left) and a novel molecular ferroelectric (BTA, middle) that can form hydrogen bonded columnar marcodipoles (right).
Our activities focus on the characterization of materials and devices and -importantly- the understanding thereof.
Responsible for this page: Anna Maria Uhlin
Last updated: 02/08/15