The SWiTch joint project, funded by the German Federal Ministry of Education and Research (BMWK) and carried out until 30 June 2022, aimed to bring perovskite‑silicon tandem solar cells from laboratory record performance to industrial production. Oxford PV Germany GmbH led the effort, with Fraunhofer ISE and Meyer Burger providing technical and process support. During the project’s final third and its extension, new suppliers were engaged to secure the continuation of the SWiTch programme.
The technical work was organised into nine work packages. Work package 2 focused on transferring and optimising standard plasma‑enhanced chemical vapour deposition (PECVD) and physical vapour deposition (PVD) processes for the heterojunction technology (HJT) bottom cell and for the perovskite top cell. The optimisation of the PVD interlayer yielded more stable process conditions and enabled the production of tandem cells with excellent electrical characteristics. Laser‑cutting experiments demonstrated that edge effects could be reduced, leading to efficiency gains of more than 5 % for certain cell variants. A new surface topography concept, applied to the HJT bottom cell, produced high open‑circuit voltages (Voc) that were successfully combined with the high Voc of the perovskite top layer, achieving tandem efficiencies above 27 % on full‑wafer industrial formats.
Work package 3 addressed the first industrialisation of perovskite top cells and tandem cells. By adapting laboratory concepts to a quasi‑industrial pilot line, the project increased the maximum throughput in several stages, moving from laboratory‑scale production to a production‑ready process. The resulting tandem modules exhibited very good stability under damp‑heat, light‑induced degradation (LeTID), and thermal cycling tests, confirming the robustness of the PWSK‑HJT technology for small‑format modules.
Fine‑line metallisation and IV measurement (work package 4) confirmed that the electrical performance of the cells remained high after integration into modules. The module design and production (work package 6) demonstrated that the tandem cells could be assembled into modules without significant loss of efficiency, maintaining the >27 % figure in module form.
The project also included a techno‑economic assessment (work package 7) and a reliability study in climate chambers (work package 8). These analyses showed that the production costs of the tandem technology could be competitive with conventional high‑efficiency silicon modules, while the reliability tests confirmed long‑term stability under realistic operating conditions.
Throughout the project, Oxford PV took over project coordination during the extension phase after Meyer Burger’s sub‑project concluded. Regular biannual meetings and interim reports kept all partners aligned, and the collaboration with Fraunhofer ISE and Meyer Burger ensured that process knowledge and equipment were shared effectively. The project’s outcomes, including the demonstration of >27 % efficient perovskite‑silicon tandem cells on full‑wafer industrial formats and the successful scaling of production throughput, provide a solid foundation for the commercial deployment of this promising technology.