Upgrading a silicon (Si) solar cell with a second solar cell made of a metal halide perovskite (Pk) is the most promising route to continue the learning curve of photovoltaic (PV) in the medium to long term. Pk materials can be deposited at low temperatures, involve elements that are available in sufficient quantities for mass production, and yield highly efficient solar cells in the lab, up to 25.7% on 0.1 cm2 in a single-junction, and up to 31.25% on 1 cm2 when combined with Si in a tandem. However, the technology will contribute to the energy transition only if these high performances can be replicated on industrially meaningful, scales (>>100 cm2) and if operational lifetimes can be extended to approach those of Si PV (>20 years). RADICALS aims to make key contributions on these points by demonstrating Pk/Si tandems yielding i) efficiencies of >30% on >100 cm2 and ii) long operational lifetime (indoors and outdoors). To do so, we will first build an in-depth understanding of the working principles and optimal growth conditions of the Pk and contact materials. More specifically, we will focus on self-assembled monolayer (SAM) contacts due to their excellent performance in lab-scale Pk cells. The investigation of this family of materials will also require the development of innovative modelling and characterization methods. Based on this understanding, we will then devise new classes of SAM materials to improve performance and stability, first of small-scale prototypes. We will then scale-up the deposition of the newly developed SAM and Pk materials, targeting high deposition throughput, robustness to defects, reproducibility, and high coating quality on M6 Si wafers. The small and large-scale PV devices will then be exposed to various operational stresses, both indoors and outdoors, to identify and mitigate degradation pathways. RADICALS combines the strengths of the groups of four applicants and two project partners. EPFL PV-LAB (main applicant), thanks to its expertise in highly efficient small-scale Pk/Si tandems and their characterization, will lead device integration tasks. KTU, who developed the SAM contacts used in the last two Pk/Si tandem records, will lead the development of the new contacts, supported by the partner CSEM NANO, who will focus on the characterization and optimization of SAM-treated surfaces. ZHAW and the partner FLUXIM have access to a large set of optical and electrical characterization methods coupled with multiscale modelling software, a knowledge that will be used here to understand performance-loss pathways across multiple length-scales. Finally, the co-applicant CSEM PMD will validate the project advances by demonstrating large-area Pk/Si tandems (>100 cm2) that reach the targeted performance and operational stability.