Partners: Merck KGaA, Darmstadt, Schott AG, Mainz, Konarka Technologies Germany, Nürnberg, Varta Microbatteries GmbH, Technische Universität Ilmenau, Universität Oldenburg, Institut für Physik, Uni Karlsruhe, Lichttechnisches Institut, Zentrum für Sonnenenergie- und Wasserstoff-Forschung, Stuttgart

Description: The project aims at flexible organic solar cells or modules that can be produced in a cost-efficent printing process. After four years of research and development, optimized modules for certain photovoltaic applications, that have the potential to compete with alternative technologies, will be fabricated.

This project is part of the organic photovoltaics (OPV) funding initiative by the BMBF to break through technological and economic barriers for the OPV-technology within the next four years. Companies and qualified research institutes / universities are organised along the value creation chain and are working together in application oriented OPV research and development.
Some goals of the partners until 2012 are:
• Development and evaluation of organic semiconductors for power conversion efficiencies above 10 %
• Development of a printable tandem type technology based on the combination of a “low bandgap” and a “wide bandgap” polymer
• Development and evaluation of printable, environmental stable electrode-materials and –buffer layers, that ensure a lifetime of 3-5 years
• Development and evaluation of production technologies and processes for an industrial fabrication
• Market-driven specifications for a cost-efficient production based on a printing process on flexible substrates and implementation of the developed modules into selected demonstrator applications

The main focus of our group is the interface for the serial connection of both subcells in a tandem solar cell. The understanding of the charge carrier recombination at the interface is of crucial importance for the function of such a device since it has to be ensured that a lossless recombination of the charge carriers can occur at the interface.
Therefore we investigate electrically doped materials that can be processed from solutions. Interesting material classes are organic polymers as well as inorganic colloids that can be dispersed in various solvents allowing for the fabrication of an all solution processed tandem solar cell.
The tandem cells are manufactured and characterized under nitrogen atmosphere in the clean room of the LTI. To determine their quality the jV-characteristics are measured. Furthermore an external quantum efficiency (EQE) measurement for tandem solar cells is going to be set up.
For a deeper understanding of the physical processes in such a complex device a simulation model of a tandem cell will be developed in parallel. Following this approach it will be possible to calculate both, the optical and electrical properties of tandem cells that can be verified in the experiment and thus contribute strongly to the development of highly efficient tandem solar cells.