Advanced Selective Contacts for Monolithic Tandem Interconnection

Silicon bottom cell with TOPCon technology being loaded off a carrier after PECVD deposition.

Silicon Bottom Cells for Tandem Photovoltaics

In order to successfully bring tandem technology to the market, it makes sense to build on a mature technology which is well-established on the market. In the photovoltaic industry, the most established technology is the crystalline silicon solar cell. Due to its band gap properties, silicon solar cells are ideally fitted to function as the bottom cell in a tandem solar cell. However, the design criteria for a silicon bottom cell differs from those of a standard silicon cell. At Fraunhofer ISE, we have many years of experience in the development of silicon solar cells from the laboratory to industrialization stage. We effectively apply this know-how to develop and adapt silicon solar cells for tandem applications and create customer-specific solutions. 

Research & Development

Equipped with an excellent state-of-the-art infrastructure and many years of expertise, Fraunhofer ISE offers a wide range of R&D services to meet the challenges facing the development and optimization of suitable silicon bottom cells for tandem applications. We optimize cell designs with consideration to the particular requirements of silicon solar cells. Our R&D portfolio for tandem solar cells includes: 

Optimization of Light Trapping for Long Wavelength Photons

We use numerous surface structuring and conditioning methods ranging from the nanometer to the micrometer scale and have an extensive characterization measurement platform at our disposal. Our long-standing expertise ranges from the simulation of photonic structures up to the simulation of entire modules, e.g. Optos project.

Adaptation of Cell Structure for Monolithic Connection

We develop a wide variety of electrically conductive and passivating contact systems that enable loss-free charge transport between the partial cells.

Customized Solar Cell Prototypes

Due to the unique technology portfolio of our laboratories, we are able to offer our customers  many different possibilities to realize special solar cell prototypes, which we can optimize and adapt according to customer specifications.

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© Fraunhofer ISE
High temperture furnace for diffusion, oxidation and annealing up to M12 wafers possible.
Maskless aligner
© Fraunhofer ISE/Foto: Dirk Mahler
Maskless aligner for the photolithographic structuring of wafers for the fabrication of high-efficiency silicon and III-V solar cells.
© Fraunhofer ISE
Ion Implanter for the implantation of different doping species like B,BF2, H, Si and further elements.

Technology Assessment

Also in this area, we can provide our customers with reliable economic and technological assessments of their technology and cell concepts at a very early stage in the development process using our collective expertise. 

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Further information on this research topic:

R&D Infrastructure

Center for High Efficiency Solar Cells

R&D Infrastructure

PV-TEC – Photovoltaic Technology Evaluation Center

Research Topic

High-Efficiency Silicon Cell Fabrication and Analysis

Research Topic

Technology Assessment