26.10.2021 | Organic solar cells
A technology for the future?
Today's PV installations are mainly designed based on silicon solar cells. Researchers and industry are working on the development of organic solar cells. Organic solar cells are light, flexible, eco-friendly and inexpensive to manufacture. In terms of efficiency, they do not yet match the performance of silicon-based solar cells. However, research is making progress in this area.
In addition to crystalline and amorphous solar cells, more information here, solar cells can also be made from organic compounds. In principle, "Organic Photovoltaics" (OPV) functions in the same way as crystalline modules and the solar power is generated through organic molecules or polymers. OPV comprises various materials from organic chemistry, i.e. hydrocarbon compounds. Organic solar cells are also referred to as polymer or plastic solar cells. The electrodes contain metal or inorganic oxides, for example indium tin oxide.
There are countless ways to manufacture organic semiconductors. Researchers have to find the best materials to achieve the highest possible degree of efficiency. That can only be determined through a trial and error process.
Advantages and disadvantages of organic solar cells
The comparison between OPV and common crystalline solar cells reveals a range of advantages and disadvantages.
Positives:
- The manufacture of organic solar cells is much less energy intensive as compared to that of crystalline solar cells because no high-temperature process is required. OPVs are light, flexible and owing to their inexpensive manufacturing costs, much cheaper than silicon-based solar cells.
- Very little material is needed to manufacture organic solar cells. OPVs can be applied to stiff or flexible materials. Since no harmful substances are used in the manufacturing process, organic solar cells are very environmentally friendly.
- OPVs have a very broad light spectrum and also work effectively under low light conditions.
Negatives:
- The efficiency of organic solar cells is much lower as compared to common solar cells. On average, efficiency is about 7 to 8 per cent, whereas silicon-based solar cells have an efficiency rate of about 20 per cent. Nevertheless: Under laboratory conditions significantly improved results have been achieved using materials from synthetic organic chemistry. The Fraunhofer ISE in collaboration with the University of Freiburg's Materials Research Center was able to achieve an efficiency rate of 14.9 per cent.
- The surface requirements for OPV are high. In addition, the impacts of weather and long-term radiation on the performance of organic solar cells has not been sufficiently explored.
A wide range of applications
Owing to their specific characteristics, organic solar cells can be used in many areas. They can be integrated into façades and buildings. Thanks to their transparency, they can also be used on glass surfaces and, as a result, offer interesting fields of application for the building materials and auto industry.
Organic solar cells also perform well under low light conditions. As a result, OPV technology is important as an electricity source in the Internet of Things (IoT) because it is particularly efficient indoors and in artificial light environments.
Thin film OPVs can also be used as coatings for clothing. The power generated in this way can, for example, charge a smart phone.
Solar cells with a future
Researchers are currently working under high pressure to increase the efficiency of organic solar cells in order to reduce this decisive disadvantage in comparison to silicon-based solar cells.
The potential is certainly there. Common silicon-based modules, which currently have an efficiency rate of about 20 per cent, are limited in their development potential. For physical reasons, they can only use approximately 30 per cent of the incident solar radiation, which sets strong limitations on increasing efficiency. This barrier does not exist for organic solar cells. New materials are continuously being developed and no one knows their exact characteristics. So-called tandem solar cells are much easier and inexpensive to realise. Tandem solar cells are made of several semi-conductor layers that use different parts of the light spectrum. Organic semiconductors are applied in layers. Multi-layer solar cells can therefore be manufactured quite easily.
Photovoltaic experts think organic solar cells will become established in the long term. Professor Andreas Bolt, Head of Research at Fraunhofer ISE, is convinced that together with partners from industry OPV can be developed to market maturity. "With its flexible application possibilities, this technology, is an important, long-term component for the urgently needed expansion of photovoltaics as an important pillar for energy generation in a sustainable system."
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