Design of Graded-Refractive Index Superlattice ARC Using PDMS and TiO2 for Enhanced Perovskite/Si Tandem Solar Cell Efficiency

Abstract

Anti-reflective coatings (ARCs) are essential for improving light absorption in perovskite/silicon tandem (PST) solar cells, yet conventional single- and double-layer ARCs often suffer from refractive index mismatch that causes reflection at each interface. To address this issue, we propose a graded- index ARC based on a nanoscale superlattice structure formed by alternately stacking thin PDMS and TiO₂ layers, followed by a textured PDMS capping layer. This design enables a gradual refractive index transition from 1.4 (PDMS) to 1.9 (IZO), the first layer that light encounters in the p-i-n PST cell. By optimizing the layer thicknesses, the proposed ARC reduces Fresnel reflection and enhances broadband light coupling into the device. Optical analysis and device measurements confirm that the graded-index ARC significantly improves light absorption in both subcells, resulting in increased Jsc and PCE compared to conventional ARC structures. These results demonstrate the effectiveness of refractive- index-engineered ARCs for high-efficiency tandem solar cells.