This deliverable focuses on the development and production of a selected encapsulant for perovskite/Si tandem solar cells, building on earlier material screening in D6.2. Yparex refined a thermoplastic polyolefin encapsulant based on silane grafted polymers and produced films at lab scale with varying thicknesses to identify optimal performance. The work includes the definition of the production process for both the grafted polymers and encapsulant films, as well as initial validation through partner feedback, confirming compatibility with tandem devices. These results provide a basis for further optimisation of encapsulant thickness and processing conditions to support stable, low-temperature module integration.