Silicon-Based Tandem Solar Cells and Modules

We develop various types of silicon bottom solar cells for use in silicon-based tandem solar cells. The silicon heterojunction (SHJ) technology is our baseline for our perovskite-silicon tandem development. We use both active bottom solar cells and so-called ohmic substrates, which offer advantages for easier characterization. 

In addition to the SHJ baseline, our main focus is on the development of TOPCon-based bottom solar cells. Here, we concentrate on both the Silicon solar cell topics (surface passivation, metallization) and the interfaces between silicon and the various top cells.

In our laboratories, we can realize different wafer and sample sizes to support both laboratory developments and full-area industrial scaling activities. 

Our R&D Services Include:

• Manufacturing and development of SHJ bottom solar cells
• Development of TOPCon-based bottom solar cells
• Development of customized contact layers 
  • TCO-based recombination layers
  • Poly-Si tunnel diodes
• Development and production of small-scale laboratory cells (active cell area e.g. 10x10 mm² or alternative formats) 
• Development and production of full-format bottom cells (up to M12)

We develop, optimize, and scale materials, processes, and perovskite-silicon tandem solar cells as a complete product. We already focus on the scalability of our tandem solar cells at the laboratory scale. For a research process that is aligned with industrial standards, we work with the Pero-Si-SCALE technology platform (Pero-Si-SCALE – technology platform for scaling perovskite-silicon tandem solar cells and modules – Fraunhofer ISE), which enables the testing of processes and materials on industrial M12 wafers. We have an extensive laboratory infrastructure for all our research activities.

With regard to the perovskite sub-cell, our research focuses on the hybrid deposition route. We also have extensive expertise and the appropriate laboratory infrastructure for the full evaporation process and for wet-chemical processes. We have demonstrated efficiencies of over 31% on silicon cells with the micrometer-sized texture commonly used in industry.

Our R&D Services Include:

• Evaluation and comparison of new contact layers, passivation layers, absorber materials and deposition methods
• Integration of new layers and materials in tandem cells
• Support in the design of equipment for the production of perovskite-silicon tandem solar cells

Investigation and Optimization of Tandem Modules

Our research focuses on analyzing the long-term stability and performance of tandem modules of various designs as well as their materials and individual components. In this function, we act as an essential link between module development, production and application in the field. 

Degradation Modeling and Prediction 

By using advanced degradation modeling, we are able to precisely describe and predict the wear and aging processes of new types of tandem modules.  

Support with Module Development 

Thanks to our extensive technical equipment and many years of expertise, we offer our customers comprehensive support in the development of modules. This also includes the reliable identification of suitable components. We develop innovative quality assurance procedures and carry out comprehensive product tests to ensure the usability and reliability of innovative tandem modules. 

Precise Performance Determination 

As an ISO/IEC 17025 accredited calibration laboratory, we are able to determine the performance of tandem modules precisely and reliably in accordance with international standards. 

Our R&D Services Include:

• STC measurements to determine the I/U characteristic of tandem modules 
• Reliability assessment of tandem modules and damage analysis 
• Analysis of long-term stability and performance 

Based on decades of experience in calibrating solar cells and modules, we can precisely  determine the performance data of tandem solar cells. To do this, the cells with different sizes up to the industrial scale are illuminated with spectrally adapted and very homogeneous radiation fields. Tandem solar cells with up to 6 pn junctions can be measured and calibrated at Fraunhofer ISE under almost any spectral conditions. In addition to solar cells for terrestrial flat-plate module applications, we also measure those for concentrator applications and solar cells for space. Supported by cell simulation and characterization, new measurement procedures have been specifically improved and adapted to the needs of novel solar cells in recent years.

Our R&D Services Include:

• Calibration of III-V based multi-junction solar cells
• Calibration of perovskite silicon tandem solar cells
• Calibration of perovskite-perovskite tandem cells
• Performance determination of novel tandem solar cells made of a wide range of materials

The interconnection of temperature-sensitive and thermomechanically demanding layers, as found in some tandem solar cells, poses particular challenges..

We are researching the optimization of standard processes and evaluating suitable materials to ensure reliable connection and module integration. To this end, we are developing low-temperature-based solutions for interconnecting the cells and adapted lamination processes. For moisture-sensitive tandem solar cells, we are adapting the bill of materials (BOM) and developing and optimizing edge sealing concepts. Our research focuses on low costs, mechanical stability and electrical performance.

Due to the diverse requirements of tandem solar cells, we pay particular attention to a comprehensive characterization of the contact points, but also to the solar cells themselves. Various methods are available to investigate the interaction of the connection processes with the sensitive microstructure of the layers and the subsequent processes during module integration (lamination), thus improving the long-term stability of the modules.

Our R&D Services Include:

• Evaluation of materials and processes
• Production of prototypes and small series as well as development of cost-effective and reliable material and process combinations (BOM development)
• Consultancy and analysis of the compatibility of materials and processes
• Detailed characterization of materials using thermal, chemical, microscopic and mechanical methods

Detailed knowledge of the physical processes in tandem solar cells is essential for developing such cells. We are therefore developing measurement methods and simulation models to analyze individual layers and interfaces in tandem solar cells. Based on our many years of expertise in technology and measurement technology, we have detailed knowledge of solar cell structures and their physics, measurement concepts and simulation methods, as well as extensive data collections on solar cell parameters. In addition, we use powerful machine learning and artificial intelligence approaches for data analysis.

Our R&D Services Include:

• Development of measurement devices and analysis methods to improve materials and solar cells from the laboratory to production
• Development of state-of-the-art simulation methods for analyzing tandem solar cells
• Material and cell analysis from laboratory cells to industrial cells
• Automated data analysis and image processing / artificial intelligence to develop a digital twin

III-V semiconductors cover a wide spectral range of the solar spectrum and are therefore ideally suited to efficiently convert the visible and near-infrared range of the solar spectrum into electricity. In combination with silicon, highly efficient tandem solar cells can be realized with two or three sub-cells. We develop III-V on silicon solar cells by direct epitaxy and via wafer bonding or gluing.

In the direct epitaxy, GaP is first grown on silicon and then the lattice constant in the ternary material GaAsP is varied so that absorbers with a band gap between 1.4 eV (GaAs) and 1.9 eV (GaInP) can be produced.

In the wafer-bonded structures, we first grow the III-V semiconductor layers on gallium arsenide and then transfer them to a partially processed silicon sub-cell. The production requires cost-effective processes for the growth of the III-V layers, for the transfer of the layers, which are only a few micrometers thick, the bonding or gluing technology and for the recycling of the expensive GaAs substrates.

Our R&D Services Include:

• Epitaxy of III-V semiconductors directly on silicon with diameters of up to 300 mm (example: GaP nucleation on silicon, GaPN, GaAsP, GaAs, GaInP)
• Characterization of defects in III-V semiconductor layers (e.g. antiphase domains, stacking faults, misfit dislocations) Characterization of III-V solar cells and modules
• Processing and process development for III-V components on silicon Process technology and device fabrication