Silicon heterojunction (SHJ) solar cells represent a new generation of solar cells based on crystalline silicon, with which very high efficiencies can be achieved. The IMD-3 is involved in material and process development of the various thin films in solar cells, both for SHJ single junction cells and in combination with perovskites in perovskite-SHJ tandem solar cells. The development and existing infrastructure range from the wet chemical pretreatment of crystalline silicon substrates, the deposition of various functional thin films using, for example, plasma-assisted chemical vapor deposition or sputtering, to various methods of post-treatment of the layers. The process development is accompanied by a wide range of optical, electrical and microstructural characterisation methods in order to resolve the smallest changes in material behaviour and correlate them with the solar cell performance.