In the »Center for Emerging PV Technologies«, we are working on the next-generation solar cell technologies, placing particular emphasis on organic and perovskite solar cells. Both technologies have in common that the materials used can be applied from solution at low temperatures by coating and printing processes. This makes production on roll-to-roll equipment possible, thus opening up enormous potential for large production volumes and low manufacturing costs.
Organic solar cells do not require the use of toxic substances such as heavy metals and can achieve very good life cycle assessments, due to their extremely low material and energy consumption during manufacture. In addition, their manufacture is RoHS-compliant (Restriction of certain Hazardous Substances) as set down by the EU. Due to their special absorption properties, organic solar cells are particularly suitable for transparent solar cells, as they offer high imaging quality and adaptable spectral absorption. Some examples of applications are solar active windows in buildings and vehicles or protective films in agriculture.
In the field of perovskite solar cells, remarkable progress has been made in recent years. The efficiency is steadily increasing, so that high efficiencies of over 25% have already been achieved for small laboratory cells. Perovskite solar cells are also used as top cells in tandem solar cell structures together with a bottom cell made from the established crystalline silicon technology. This promising perovskite-silicon solar cell enables a further quantum leap in efficiency, compared to the conventional pure silicon cell technology, which is dominant today. Also, a tandem solar cell that combines two perovskite absorbers with different band gaps shows great potential for increasing efficiency and reducing costs.
Services and Expertise
Evaluation of Materials and Components
We have laboratory lines for processing under inert gas. Currently, three glovebox lines with spin coaters, vacuum evaporators and various automated basic characterization processes are in operation. Solar cells are produced on these lines under exclusion of oxygen and water in order to test and optimize new materials and layer stacks.
Characterization and Modeling
To identify the factors limiting the efficiency of solar cells and modules, various electro-optical characterization techniques are used. In addition to current-voltage characteristics at various intensities and temperatures, these include electro- and photoluminescence measurements (both steady-state and transient), LBIC (Light Beam Induced Current), and DLIT (Dark Lock-in Thermography). Imaging techniques can also be used for these methods. Numerical simulations of the various processes occurring in the solar cells allow us to further our understanding.
Upscaling and Manufacturing in Roll-to-Roll Processes
Fraunhofer ISE develops layer systems, PV module concepts and production processes which are suitable for cost-effective roll-to-roll production. Even for medium production volumes, material costs are the largest factor in roll-to-roll production costs. Thus, our major focus here is to develop manufacturing solutions that are cost-effective, available and compatible with safety requirements. Upscaling can be carried out at various development stages, from spin-coated laboratory modules up to demonstrators produced on sheet coating and flatbed screen printing systems and large PV modules produced on film rolls with the roll-to-roll process.