The race for the best solar cells material has a new candidate: Perowskit. No other semi-conductor has enabled researchers to succeed in achieving such a dramatic development in efficiency levels. “There is now an absolute hype surrounding Perowskit,” says Thomas Unold, head of the Institute for Technologies (Institut für Technologien) at the Helmholtz-Centre Berlin.
The mineral promises to be efficient and at the same time inexpensive. Up to now it has not been possible to combine both these characteristics: currently the best silicon cells achieve an efficiency level of over 20%, but are expensive to produce. Pigment and organic solar cells in turn can simply be printed on film, but often do not exceed an efficiency level just over ten percent.
|Thin, light and supple:
deposits a photoactive
film in wafer-thin form
onto a carrier film.
The film can thus be used
almost without any limits
to produce electricity.
Photo: Heliatek /
As a result, the high-performance light-weights could conquer the markets which were previously, to a great extent, taboo for photovoltaics. Building integrated photovoltaics for example, in short BIPV continues to be just a niche market, because the manufacture and installation of multi-functional BIPV modules is costly and expensive. Of the 3,300 Megawatt solar power output, which went online in 2013 in Germany, it is estimated that only around 100 Megawatt was integrated in building shells. A market inhibitor: the BIPV elements are mostly project-orientated variations, which in terms of size, form, material, colour, varying transparency and design, are adapted to the respective building – individuality and the high planning expenditure have their price. Perowskit cells could help to reduce costs.
In addition, the technologies which come into consideration for BIPV have previously not been efficient enough. Often modules made of thin-layer silicon are available, but they rarely reach an efficiency level of 10% – too low to be able to compete with classic silicon cells on the roof, which convert almost twice the amount of light into electric energy. They themselves are only suitable to a certain extent for building integration: they are sawn straight out of blocks because they are simply too thick and inflexible for more complex BIPV applications.
|Algae house: In the façade of the
“House with Bio Intelligent Quotient” in Hamburg algae use
photosynthesis to produce heat for the apartments. Photo:
IBA Hamburg GmbH / Johannes Arlt
However, until the promising Perowskit cells can be used commercially, the researchers still have to master several challenges. “The development is just beginning”, says Helmholtz researcher Unold. The service life is regarded as the greatest hurdle. Perowskit is sensitive and quickly degrades when it comes into contact with water. For that reason the cells must be designed in such a way, that even over a period of 20 years no moisture must be allowed to penetrate them. Leak-proof encapsulations, which were developed for organic light-emitting diodes are one possible solution.
In the meantime other promising technologies, which are currently ready for market introduction, have been able to drive forward the BIPV market. Dresden company Heliatek for example has developed an organic photovoltaic film, which can be produced both in transparent as well as tinted form. In non-transparent form it reaches an efficiency level of twelve percent, while the translucent variation has a reduced efficiency level down to around seven percent. Compared to conventional silicon modules this is low, but in the area of organic photovoltaics it sets a new record. In addition, the flexible films can be embedded in curved formats such as glass car roofs or irregularly formed façades. As dimming films are, as a rule, also in demand in vehicles and offices, there is no additional maintenance expenditure, argues Heliatek boss Thibaut Le Séguillon. As a result, competitive prices are possible, he said.
Other companies are also banking on the concept of flexible and transparent cells in organic material. The Bavarian company Belectric as well as Crystalsol from Austria for example are working on printed polymer cells. Polymers are chemical combinations of long molecule chains, which can be enriched in a solution and then printed. Heliatek in contrast uses oligomers as light collectors, in other words shorter molecule chains. In addition, it does not print, but vaporizes them in a vacuum onto a carrier film. Currently Heliatek is still operating pilot production. With solar films from this production line the company has just set up the first window façade in Dresden. The next step planned by the company is commercial production with an annual capacity of 100 Megawatt.
|Field-tested showcase project: The roof of Berlin's main rail
station clearly illustrates the advantages of BIPV: the
modules generate electricity and at the same time transmit
light. Photo: BSW-Solar / Paul Langrock
It is not only due to the cooperation with Heliatek that AGC Europe is regarded as a trailblazer for the glass industry. Its factories are home to a fully-integrated production line which not only covers the production of glass but also its coating and further processing. Various functional coatings are available to photovoltaics manufacturers, for example electrical contact layers for thin-layer modules. A similar solar-orientated concept has otherwise previously been pursued solely by East German company F-Solar. They, too, have extended their production line at their own company to include coating systems.
At glasstec 2014 in Düsseldorf, from 21 to 24 October 2014, the world's largest and most international trade fair for the glass sector, companies will have the opportunity to pave the way for further cooperations. In this connection, experts from the solar power and glass industry will come together from 20 to 21 October 2014 at the “Solar meets Glass” conference to enter into an exchange about advances in the production of solar glazing and modules as well as the material and costs. The “glass technology live” special show, which has been organized by the Institute of Building Technology, Construction and Design (Institut für Baukonstruktion) at Stuttgart University, is focusing among other things on the interface between solar technology and glass. Here, using the example of large-format façade mock-ups and scale models, the latest developments in the façade and energy sector are presented, including innovations in photovoltaics and solar thermal energy.
At “glass technology live”, however, projects will also be presented which extend beyond pure solar applications. Such as for example the so-called BIQ – the abbreviation stands for “House with Bio Intelligent Quotient”. In its bio-reactor façade algae grow on glass panels and use the combination of light and carbon dioxide to produce biomass and heat. The heat is supplied to the 15 apartments directly for heating purposes via heat exchangers, while the bio mass is skimmed off. It is used to obtain biogas, converted by a fuel cell into electricity and additional heat. All the energy required to produce electricity and heat is created from regenerative sources, fossil fuels are not used, according to the construction company responsible for the project, Otto Wulff.
Energy-generating house façades such as those demonstrated by the BIQ could play a key role in the energy turnaround in the cities. Researchers and companies are working flat out on concepts and technologies, which transform building shells into efficient power stations. In this process the glass industry could assume a key role. By working more closely with the manufacturers of solar modules and collectors it could further accelerate innovations.
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