Module integration of III-V compound semiconductor/silicon two-junction solar cells with three and four terminals

• Applicant: Dr. Henning Schulte-Huxel
• Subject Area: Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives ; Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: from 2016 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 329888662

Photovoltaic modules with multijunction solar cells convert solar irradiation more efficiently to electrical energy than present modules. In recent years, silicon-based multijunction cells came into the focus of research, since they offer a cost-effective implementation of this technology. The multijunction cells consist of two or more subcells, which are stacked on top of each other. The annually generated energy yield depends on one hand on the properties of the subcells and on the other hand on their interconnection. It is possible to increase the energy yield by up to 20% if the cells are not connected in series, but contacted separately. The latter can be achieved by using tandem cells with three or four terminals. However, there are a lack of adequate interconnection concepts for these solar cells. To close that gap is the aim of this research project.In the first part of the project, the properties of the subcells will be determined experimentally and by devices simulations. On basis of these results, the impact of various illumination conditions, as well as the requirements of the interconnection for different schemes, will be analysed using electrical and optical simulations in order to maximize the cell and module power.The outcome of these analyses will be used in the second part of the project to develop interconnection designs for multijunction solar cells with three and four terminals. It has to be taken into account that, for most applications, photovoltaic modules without concentrating optics are advantageous and that silicon solar cells featuring both contacts on their rear side convert sunlight more efficiently. Therefore, the interconnects have to be designed in such a way that they cover only a small fraction of the illuminated module surface. Further, the interconnection scheme has to be able to contact the two rear contacts of one subcell, as well as one or two of the contacts on the sunny side of the solar cells. To address these requirements, a multilevel metallization will be implemented that is located underneath the solar cells. The applicability of the interconnection scheme will be shown with proof-of-concept modules. These modules are characterized under various illumination conditions in order to verify the simulations of the first part and to show the advantage of the developed interconnection in comparison to multijunction devices with the subcells connected in series. Thus, the aim of this project is to close the gap in the present research and development of new photovoltaic technologies in order to contribute to an increased usage of renewable energies.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Dr. Adele Tamboli