// Tandem thin-film photovoltaics: Sustainable perovskite/CIGS solar modules from industrial processes (PVKIS)
The efficiency of solar modules can be further increased by combining two solar cells with complementary spectral absorption ranges in a tandem configuration. Due to their high band gaps, the novel perovskite solar cells are ideal tandem partners for Cu(In,Ga)Se2 (CIGS) cells.
In order to innovatively expand photovoltaics and secure Germany's technological lead in this field, highly efficient PV materials and concepts must be further developed to industrial maturity. PVKIS focuses on sustainable tandem modules from industrial processes consisting of a CIGS bottom cell and a perovskite (PVK) top cell. The PVK/CIGS tandem modules are to be designed in a 2-terminal architecture (see figure).
The basis for development in PVKIS are industrially manufactured CIGS thin-film modules, which are already established on the market. Building on current tandem laboratory samples developed at HZB and KIT, monolithically interconnected tandem modules are to be developed within the project period that achieve an efficiency of 24% on 5x5 cm² substrates. To this end, various monolithic interconnection technologies are being tested, for which the corresponding laser structuring processes are being developed. These exemplary mini-modules will have the full functionality of a large-format module and will be manufactured exclusively using scalable processes that allow direct upscaling to industrial processes. There is a strong focus on the development of scalable deposition methods for the layers of the PVK cell. No deposition method suitable for large areas has yet become established, but there are three processes (inkjet printing, slot die coating, and vapor deposition) that are scalable in principle and have already demonstrated efficiencies greater than 20% in individual PVK cells. None of these processes has yet been used in PVK/CIGS tandems. The challenge here is to achieve conformal coatings on the relatively rough surface of a CIGS cell. As part of the project, the three methods mentioned above for depositing the PVK cell on large areas are to be further developed. The ZSW will test the coating using the slot die coating process on CIGS, initially on a small area and in an inert gas atmosphere, and also on a small scale directly in (humidity-controlled) ambient air.
