Heliatek, in a joint R&D-project with the IAPP (Technische Universität Dresden, Germany) and BASF SE, has achieved a record value for organic solar cells based on vacuum deposited small molecules.
According to Heliatek, which was founded in 2006, a power conversion efficiency of 5.9% for an active area of 2 cm² has been confirmed by the National Renewable Energy Laboratory (NREL).
The highest previously confirmed value for organic solar cells with an active area exceeding 1cm2 was 5.4% for a polymer-based device.
The record value was achieved with a tandem solar cell. In order to make optimum use of the light with different colours included in the sun spectrum, two different dye pigments are combined. To absorb blue and green light, an organic “oligomer”, developed by Heliatek in cooperation with the University of Ulm, is used, while yellow and red light is absorbed by a dye pigment synthesized by BASF.
The objective of Heliatek, BASF and Bosch within their joint development agreement is to further increase the device efficiency to 9-10% and establish a first pilot production line by 2011.
An oligomer is a polymer with a short chain of well defined length and it can be thermally evaporated in vacuum without decomposition due to their light weight thus enabling the deposition of ultrathin layers by a vacuum evaporation process. The novel solar cell is based on Heliatek’s proprietary p-i-n tandem cell architecture.
The tandem solar cell reaches an open circuit photovoltage of 1.6V and a fill factor of 65%. The width of the certified device corresponds to a typical stripe width for thin film PV modules with integrated series interconnection.
The required layer thicknesses are in the range of 100 nanometer (1/10000 mm). Thus only about 1 gram of organic semiconductor materials is required for 1 square meter of solar cell area. To establish a production process, synergies with the already well established technology for large area deposition of small molecule organic light emitting diode (OLED) displays can be used.
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