Organic Photovoltaics

Organic photovoltaics offers unique potential for the generation of environmentally friendly electrical energy. The semiconducting materials essentially consist of hydrocarbons, ranging from small molecules to polymers. The layers of organic solar cells are around 1000 times thinner than crystalline silicon solar cells, ranging from a few nanometers for certain contact layers to several hundred nanometers for the light-absorbing layers. This makes them extremely light, flexible and unbreakable, determined solely by the packaging. Due to the low material consumption, the simple processing with printing and coating processes and the avoidance of critical elements such as lead or cadmium, the ecological footprint is extremely small.

OPV technology has the potential to further increase CO₂ savings through photovoltaics and drastically reduce energy recovery times. As the materials are carbon-based, it is even conceivable in the long term to produce them synthetically from CO₂, provided that such technologies, such as Power-to-X, can be established in the future. The molecularly shaped optical properties open up unrivaled adaptability, so that a wide variety of types of solar cells can be developed, from classic single-junction solar cells with efficiency potential of at least 20% (19% has already been achieved in the laboratory), to multi-junction solar cells with potential for even higher efficiencies or solar cells specially adapted to artificial light sources, to spectrally selective solar cells that are highly transparent in the visible spectral range and use UV and infrared light to generate electricity. As a result, this technology can enable innovative products such as floating photovoltaic films, electricity-generating awnings, window panes and greenhouses, particularly in integrated photovoltaics.  In the short term, initial applications as an energy source for wireless sensor technology in the areas of production, logistics and smart homes appear feasible. 

This extraordinary potential motivates us to work with our partners to tackle the existing challenges in terms of efficiency, long-term stability, scaling up to modules and production processes in a targeted and application-specific manner.

New organic semiconductors and contact materials are continually being synthesized all over the world. This makes continuous screening of the most promising materials indispensable. Our attention is focused not only on the highest efficiency values, but also on long-term stability and compatibility with production-relevant cell stacks and processes. The most suitable materials are identified for various applications.

Our R&D Services on this Topic Include:

• Testing of materials and components for use in organic solar cells
• Benchmarking in reference cell stacks
• Development of production-relevant cell concepts

Organic photovoltaics offers a unique potential for modules with high visual transparency. Since organic semiconductors absorb only a limited bandwidth of light due to their molecular nature, Materials can be produced that strongly absorb near-infrared light but hardly any visible light. This is not possible with other technologies based on band-edge semiconductors such as silicon, inorganic thin-film materials or perovskites due to fundamental differences in the material properties. The spectral selectivity of organic semiconductors theoretically allows the production of completely transparent photovoltaics with a potential efficiency of 20%. In addition, fine laser structuring can be used to produce modules with barely visible structures. On the terawatt scale, highly transparent OPV can be used in the sections of agri-photovoltaics, building integration and e-mobility. We are working hard to exploit this potential.

Our R&D Services on this Topic Include:

• Development of highly transparent front electrodes and optically selective rear electrodes with high transmission in the visible spectrum and high reflectivity in the near-infrared spectrum
• Application-specific optimization of the layer stack with regard to the desired degree of transparency and the layout of modules
• Manufacture of demonstrator modules

From world-record modules produced under laboratory conditions to flexible OPV modules manufactured entirely using roll-to-roll processes, we can process modules on rigid and flexible substrates using various coating methods in air and under inert gas. Our development activities focus on scalable processes that use inexpensive and harmless materials. In this context, cell stacks, circuitry and dimensions are optimized for each specific application. For example, the optimal modules for an application under indoor lighting conditions differ significantly from those to be used outdoors. The choice of organic semiconductor material, the electrode layers and the module layout then depend on such practical differences.

Our R&D Services on the Topic Include:

• Application-specific optimization of the module layout
• Development of cost-effective and robust module concepts
• Production of demonstrator modules

The requirements for long-term stability and the main influencing factors depend heavily on the respective application. Various aging tests under controlled conditions (e.g. continuous illumination with simulated sunlight or LEDs, elevated temperature) and outdoors can be used to identify the crucial factors and to improve the OPV modules in a targeted manner. From small laboratory cells to OPV modules, we can precisely determine long-term stability by measuring characteristic curves and maximum power point tracking. By recording important environmental parameters, correlations can be established and behavior at different light intensities, angles of incidence and temperatures can be determined. By determining such data and conducting a thorough characterization, the decisive factors for degradation can be identified and the component stability of OPV modules improved.

Our R&D Services on this Topic Include:

• Accelerated aging in the laboratory
• Outdoor weathering on a roof test stand
• Standard tests in the accredited test laboratory

In the long term, a thorough understanding of how organic solar cells work is crucial for the efficient further development of the technology. A wide range of characterization methods makes it possible to identify limiting factors in a targeted manner. Modeling allows hypotheses about influencing mechanisms to be tested quantitatively, thus enabling an increasingly detailed understanding to be gained. These methods also help in the section of long-term stability, both to localize weaknesses in the encapsulation and to identify degradation mechanisms.

• Electrical simulation of components (Sentaurus TCAD)
• Optical simulation (transfer matrix and RCWA)
• Electro-optical characterization to identify functional principles and limiting components in the solar cells
• Imaging techniques (thermography, spatially resolved photocurrent, electroluminescence, photoluminescence) to localize defects and optimize coatings and production processes

Further Research Projects on the Topic "Organic Photovoltaics"