Achieving Improved Light Trapping in CIGS/Perovskite Solar Cells with Grating-Enhanced Bilayer Heterojunctions: Optical-Electrical Study

This work investigates a cost-effective and less toxic alternative solar cell design: a CIGS/perovskite bilayer heterojunction integrated with photonic nanostructures. The bilayer structure reduces thermalization losses by combining a high-bandgap perovskite (CH₃NH₃PbI₃, 1.55 eV) top cell with a lower-bandgap CIGS (1.2 eV) bottom cell, enabling efficient spectrum utilization. CIGS is selected over silicon due to its direct bandgap, allowing reduced absorber thickness, lower material use, and potentially lower costs. The bilayer achieved a short-circuit current density of 25.98 mA/cm² and a power conversion efficiency (PCE) of 22.98%, representing a 15% improvement over singlejunction perovskite cells. Further enhancement is achieved with convex grating light-trapping structures, raising the simulated PCE to 25.54%. Device performance was analyzed through coupled optical and electrical modeling using the finite element method in COMSOL Multiphysics, highlighting the potential of bilayer heterojunctions with photonic gratings for high-efficiency, scalable photovoltaics.