Design and optimization of double semi-cylindrical plasmonic nanostructures for enhanced light harvesting in ultrathin CIGS solar cells

This work presents a theoretical study on ultrathin Cu(InxGa1-x)Se2 (CIGS) solar cells with an absorber thickness of only 200 nm, enhanced by plasmonic nanoparticles (NPs). The inherent trade-off reduced absorber thickness, and sufficient light absorption was addressed by investigating metallic nanoparticles of silver (Ag), gold (Au), aluminum (Al), nickel (Ni), and titanium (Ti) in spherical and cylindrical configurations. Building on this approach, a single semi-cylindrical geometry was introduced to minimize optical losses, and the inter-particle spacing was systematically optimized to maximize light trapping. Three-dimensional finite difference time domain (3D-FDTD) simulations revealed that the interaction between coupled NPs strengthens both the localized fields around the NPs and the scattered fields within the absorber, leading to more efficient carrier generation. In the optimized case, the semi-cylindrical double NPs (DNP) structure exhibited a 29% higher near-field intensity at the resonance wavelength of 731 nm compared with the single half-cylindrical design, highlighting the crucial role of plasmonic coupling. As a result, the short-circuit current density (JSC) increased from 22.50 (mA/cm²) to 31.12 mA/cm², representing an increase of 38.3%. In addition, the power conversion efficiency (PCE) increased by 40.3%, from 12.97% to 18.20%. These findings demonstrate that carefully engineered plasmonic nanostructures can substantially enhance the performance of next-generation thin-film CIGS photovoltaic devices.