Updated: Scientists to push organic solar cell efficiency

PARIS – Researchers from the Karlsruhe Institute of Technology (KIT) have launched a four-year research program that aims to improve the efficiency of organic solar cells to more than 10 percent.

Organic solar cells are cheaper to produce, lighter and more flexible than traditional silicon-based solar cells, opening new perspectives in particular for the architectural design of buildings. Solar modules can be integrated in facades and even windows. The downside is that the efficiency rate of OPV cells remains much lower than inorganic solar cells, demonstrating 15-20 percent efficient.

Led by Dr. Alexander Colsmann, head of Organic Photovoltaics Group at the Light Technology Institute, KIT, the newly-launched project uses tandem architectures. Two solar cells with complementary absorption characteristics are stacked directly on top of each other to achieve better sunlight harvesting and more efficient energy conversion.

The KIT scientists said they use novel materials, develop innovative device architectures, optimize their stability, and test the solar cells in a real-life environment. They also intend to transfer manufacturing processes from the laboratory to an industry-compatible production environment so as to promote future commercial use of their results.

Recently, Heliatek GmbH (Dresden, Germany) claimed it had pushed the record efficiency for organic solar cells higher, achieving an efficiency of 10.7 percent in a 1.1 square centimeter tandem cell. Measurements, led by independent test house SGS SA (Geneva Switzerland), showed that the cell improved efficiency under low light conditions and that the efficiency remains constant with temperature.

In a discussion with EETimes, Colsmann acknowledged Heliatek's achievements but specified that Heliatek uses a different class of materials. "They build solar cells from low-molecular weight organic molecules in vacuum processes," he stated.

Colsmann indicated that KIT uses polymers and other functional materials that can be applied in large-scale coating and printing processes. The vision is to print solar cells one day in the same fashion as newspapers are printed nowadays. With this approach, Colsmann said the project aims at significantly lowering production and consequently energy conversion costs.

Colsmann continued: "The tandem concept is a concept that, on the one hand, has been realized by a number of groups already. This means that this concept is working. On the other hand, tandem solar cells have not yet been fully understood. Calculations on basis of the currently available material classes show that tandem solar cells have a potential of up to 15 percent power conversion efficiency not accounting for further material classes being invented in the future."

In other words, Colsmann concluded, there is a lot of work to be done in order to further push the device efficiencies by really understanding the underlying performance driving mechanisms and to advance the respective printing processes towards low-cost production.


The project received a 4.25 million euro ($5.35 million) funding from the Federal Ministry of Education and Research.

It has also received the support of the Fraunhofer Institute for Applied Polymer Research (IAP), Potsdam, and the University of Queensland/Australia, which supplies new materials for organic solar cells. Merck KGaA is the industry advisor of the project.