Photovoltaics (PV) are a cornerstone of the global energy transition. Today, silicon-based solar cells dominate the market (97%), achieving average conversion efficiencies of 23% typically using 150 µm-thick wafers. The next generation of solar cells could achieve a seemingly paradoxical goal: higher efficiency with less material. Ultrathin solar cells (10x thinner than conventional ones) offer a transformative solution for material savings and reduced carbon footprint, lightweight and flexible applications. However, their performance has been limited by insufficient light-trapping to compensate for the reduced material volume. Our team has already achieved a major milestone: in 2019, we demonstrated a 19.9%-efficient ultrathin solar cell with only 200 nm of GaAs, using a nanostructured back mirror that leverages multi-resonant absorption (Nature Energy, 2019). We’ve also published a comprehensive review on ultrathin cells (Nature Energy, 2020) and derived theoretical upper bounds for light trapping (PRX Energy, 2026), opening new perspectives for ultrathin solar cells. This internship builds on these results to develop solutions for light-trapping in ultrathin solar cells. It will combine clean-room work and optical simulation, and it will explore the potential of correlated-disorder nanostructures for light-trapping using low-cost, self-assembly processes, aiming at their integration in single-junction silicon solar cells and tandems.