BiSoN and ZEBRA: ISC Konstanz´s bifacial modules displayed at SNEC show


Today’s high efficient n-PERT cell BiSoN is already in production with standard production technology. IBC technology for tomorrow (ZEBRA) can be implemented as an upgrade of existing lines. Bifacial BiSoN and ZEBRA modules up to 400W (in bifacial mode) are shown at SNEC show. ISC’s aim is not only cheap production but also enabling generation of lowest electricity prices: In order to accelerate the adoption of solar photovoltaic (PV) electric power worldwide, the levelized cost of electricity (LCOE) of PV power generation ($/kWh) must be continuously reduced. This goal can be achieved by either reducing the lifecycle cost of PV systems ($/Wp) or by increasing the amount of generated electricity (kWh) over the entire lifetime of the systems. The best solution is a combination of both approaches: ISC demonstrates this by a double-glass BiSoN PV module, and by the world’s first double-glass bifacial IBC PV module developed by the Solar Energy Research Institute of Singapore (SERIS) with ZEBRA IBC solar cells from ISC Konstanz, Germany.


ISC Konstanz has been offering the nPERT technology BiSoN since 2015. There were three technology transfer projects in that time. The latest one is Mundra Solar PV (Adani) in northeast India where the 100MW BiSoN line will start production in 2nd term 2017. BiSoN-cell to wafer transformation cost (cell CoO without wafer) is currently around 9 €ct/Wp.

From the other two BiSoN customers large PV systems are already producing electricity in large bifacial systems. For example in MegaCell´s “BiSoN Farm” La Hormiga in Chile. The 2.5MWp system showed a peak power of 3.3MW due to high albedo from the ground covered with white quartz sand.


ISC Konstanz has been working on the ZEBRA development since 2009 with Italy based company Silfab. The goal was always to reach highest efficiencies with cost effective processes only, such as tube furnace diffusions, PECVD SiNx depositions and screen printing,. Starting with 12% efficiency, ZEBRA is currently reaching 22% with wafer-to-cell transformation cost of about 10.5 €ct/Wp. This technology has been further developed in EU Project HERCULES and other projects funded by EU or Germany. A price for the best project of the year has been awarded to the EUROSTAR project ModerN-Type together with Eurotron in 2016 for the monofacial 60 cell ZEBRA module with 310+Wp resulting from that project.

400 W bifacial IBC module demonstrated at SNEC trade show

The International Solar Energy Research Center (ISC) Konstanz and the Solar Energy Research Institute of Singapore (SERIS) at the National University of Singapore (NUS) have in a collaboration successfully produced the world’s first Interdigitated Back Contact (IBC) bifacial double-glass module using industrial ZEBRA solar cells developed and fabricated at ISC Konstanz. With 60 high efficiency solar cells of 6 inches in size each, the IBC bifacial module that has been assembled by SERIS, has the potential of attaining up to 400W.

Together with SERIS, we start the bifacial ZEBRA journey. Double glass encapsulation provides the best protection to embed solar cells due to its excellent reliability and durability. Therefore, prolonged warranty of up to 30 years can be offered by the manufacturer. Incorporating the bifacial cell technology, as high as 30% additional power can be added to the double-glass module output due to reflection of sunlight from the ground.

The ZEBRA cell used in this double-glass bifacial module is an interdigitated back contact (IBC) solar cell developed and produced at ISC Konstanz, using only industrially proven process equipment and standard industrial 6-inch n-type Cz mono-Si wafers. The ZEBRA cells achieved an efficiency of 22% in the pilot production using screen-printing metallization.

The world’s first IBC bifacial module has the following unique features:

  • All back contact: This enables no shading of the cell on the front side. As a result, the cell can achieve higher current and efficiency outputs.
  • Bifacial nature: The module is able to absorb light from both the front and rear side of the module, with a bifaciality of 75%. This enables the module to absorb reflected light from the rear of the module and generate more energy. 20% more energy yield in a standard field for bifacial systems were shown.
  • Double-glass structure: The module is encapsulated in between a double-glass structure using polyolefin elastomer (POE) which guarantees long term reliability and durability.
  • Low temperature interconnections: This prevents warping of the IBC cells after heating.
  • Specially designed & customized junction box: This prevents shading of the rear surface of the bifacial IBC cells.
  • Industrially feasible solar cell and module fabrication process and equipment: This enables the module to achieve high efficiency at lower cost and means that the technology is ready for industrial production.


The world’s first double-glass IBC Bifacial Module fabricated by SERIS will be on display at the booth set up by ISC Konstanz's industry collaborators, Centrotherm Photovoltaics AG (booth #360, E3), here also together with a bifacial BiSoN module, and SPIC Xi’an Solar Power (booth #330, W1), at the SNEC (2017) International Photovoltaic Power Generation Conference & Exhibition (SNEC PV POWER EXPO), Shanghai, China, from 19-21 April 2017.

Dr Radovan Kopecek, founder of ISC Konstanz, Director of Advanced Solar Cells and Lead Scientist for ZEBRA development since 2009, has ambitious future plans for this technology: “Many people now might think that putting highly efficient IBC cells into bifacial modules does not make sense – but our consortium will prove them wrong. The ZEBRA process is extremely simple and cost-effective and so is the module manufacturing process. In large bifacial systems, this technology will lead to the lowest LCOEs ever. Bifaciality is quickly gaining popularity and, since a few weeks ago, one can now also simulate the bifacial advantage using PVsyst – such developments will give many bifacial technologies the breakthrough in the PV systems arena”.

Dr Wang Yan, PV Module Cluster Director at SERIS, who led the module cluster towards the production of this novel module technology, is very excited about the development. “The IBC bifacial module offers high front side power while providing free power from the rear side. As a result, it has the lowest LCOE potential” he explained. “The prototype module serves as a proof of concept for mass production. The next step would be to commercialize the technology.”