As part of a joint research project carried out together with the Technical University of Dresden's Institute of Applied Photo-Physics, the Dresden-based Heliatek GmbH company has achieved a break-through in organic solar-cell efficiency.
With a certified efficiency of 7.7 % over an active area of 1.1 cm2, a new record was set for organic solar cells. The previous highest certified value for organic solar cells with practical relevance was 6.1%. It too was set by Heliatek in 2009, together with its partners, the IAPP and BASF.
The certification of the cells was carried out by the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, an independent and globally recognised testing laboratory. The term "with practical relevance" usually denotes solar cells with an active area of above 1cm², as these already display all the main characteristics of large solar panels.
For around twenty years now, organic solar-cell technology has been intensively developed by many groups worldwide. The achievement of this new value represents a decisive step forward, as it is the first time organic solar cells have achieved the same level of efficiency under laboratory conditions as commercial PV cells made of amorphous silicon.
Thus the specific advantages of organic solar cells are coming now into their own: at modest cost, and with extremely low material and energy requirements and low processing temperatures, they can be deposited on inexpensive carrier materials such as glass or plastic foil. The required layer thickness lies in the region of 100 nanometres (1/10 000mm), so that less than one gram of organic semi-conducting material is required per square metre.
The so-called "p-i-n Tandem Cell Technology" developed and patented by the partners forms the basis for this success. It is based on a combination of two technologies: doped organic materials ("p-i-n technology") and the stacking of solar cells ("tandem cells"). The record-breaking cell uses organic colouring agents specially optimised for use in solar cells, whereby one agent absorbs the short-wave portion of sunlight (blue and green light) while the other absorbs the long-wave portion (red and near-infrared light).
The absorbers were developed by Heliatek and its investor, BASF (Ludwigshafen). Doped organic materials, which form the basis of the pin technology, were developed by Novaled AG (Dresden) primarily for use in organic light-emitting diodes (OLED). Heliatek thus creates synergies with the OLED technology, which has already established itself with various products on the screen display market.
Heliatek's technology is based on the thermal depositing of organic molecules within a vacuum. Production processes using vacuums are used in the semi-conductor industry and have established themselves as very stable and cost-efficient. However, the use of vacuum
depositing within the organic photovoltaic industry represents an innovation: international competitors in the area of organic solar cells use solvent-based printing processes for polymers, as these have hitherto often provided better efficiency levels and been considered cheap to manufacture.
With the new value achieved by the organic solar cells consisting of "small molecules", Heliatek has achieved a performance level which goes beyond that of polymer printing technology. Owing to more stable production processes, vacuum depositing has already won out on the global market over polymer printing in the area of organic light-emitting diodes (OLED).
Following the successful completion of a financing round to the sum of €18 million at the end of 2009, Heliatek is set to begin pilot production for the roll-to-roll manufacturing of organic solar cells. Introductory products are to hit the market at the end of 2011.
Together with its strategic partners BASF and BOSCH, Heliatek aims to increase the components' efficiency to >10%, and to establish technology for mass production.
Heliatek's activities are linked to various R & D projects in which the IAPP, the University of Ulm, Novaled AG and Fraunhofer IPMS (Dresden) are also involved. Heliatek receives public funding for these projects from the German Federal Ministry for Education and Research (BMBF) as well as from the Sächsische Aufbaubank ('Saxony Start-up Bank', SAB), using funds from the Free State of Saxony and the EU. The collaboration between Heliatek and the IAPP, which has resulted in the development of the certified components, is based on the BMBF-sponsored "Organic p-i-n Components" InnoProfile group and the research and technology platform developed therein.
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