January 8, 2016

Organic photovoltaics: TUM researchers observe molecular processes

Stephan Pröller (l.) and Dr. Eva M. Herzig in their laboratory. Here they investigate the
processes that take place on the molecular scale during the production of organic solar cells.
(Photo: Uli Benz / TUM)

(January 8, 2016)  X-rays reveal details of plastic solar cell production

Plastic solar cells are light, easy to install, and readily produced using a printer. Nevertheless, the processes that take place on the molecular scale during the production of organic solar cells are not yet entirely clear. Researchers from the Technical University of Munich (TUM) have now managed to observe these processes in real time. Their findings, which are published in the specialist journal Advanced Energy Materials, could help to improve the efficiency of organic solar cells.

The solar modules that can be seen on the roofs of many houses mainly consist of the semiconductor silicon. They are heavy and consequently costly to secure on roofs. Moreover, they do not blend in very well with their surroundings.

Organic solar cells, which consist of organic molecules like plastic bags or cling film, are an alternative to these conventional solar cells. Organic solar cells are soluble and can therefore be produced using a printer. Since they are very thin and light weight the installation of this thin light converting device in a variety of different locations is feasible, furthermore, the color and shape of the solar cells can also be adjusted. One of the current disadvantages is, however: The efficiency of organic photovoltaics has not yet reached that of silicon solar cells.

Processes at the nano level

One of the key parameters for harvesting more energy from the flexible solar cells is the arrangement of the molecular components of the material. This is important for the energy conversion because, as in the case of the "classic" solar cell, free electrons must be produced. To do this, organic solar cells need two types of material, one that donates electrons and another one that accepts them. The interface between these materials must be as large as possible to convert light into electricity. Up to now, it was not known exactly how the molecules align with each other during the printing process and how the crystals they form grow during the drying process. Like the pigments in printer ink, the molecules are initially contained in a solution.

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