Comprehensive optimization of spacer layer and dielectric coating for plasmonic solar cell

Plasmonic-enhanced light trapping by silver nanoparticles is a promising way of increasing the light absorption in solar cells and therefore, the cell photocurrent. In this paper, we applied silver nanoparticles on the rear side of polycrystalline silicon thin-film solar cells and numerically investigated interdependent effects of the spacer layer and a dielectric coating, with and without a back reflector. Two different spacer layer materials, MgF₂ (n=1.4) and SiNx (n=2), with thickness of 0, 5, 10, 20 and 30 nm, and three dielectric coating materials, MgF₂, SiNx and TiO₂ (n=2.5) with thickness of 150, 200 and 300 nm were comprehensively studied. Simulation results show that, for nanoparticles without dielectric coating and back reflector, photocurrent enhancement is higher without a spacing layer; while in presence of dielectric coating and back reflector, a thin spacer layer results in higher photocurrent enhancement. The optimal thicknesses of the spacer and dielectric layers depend on the refractive index of the chosen material. A combination of 20 nm MgF₂ spacer layer, 150 nm SiNx dielectric coating and a back reflector gives the highest simulated short circuit current enhancement of 43%. The rigorous simulation provides the insight into a mechanism of how the spacer layer and the dielectric coating material and their thickness influence the cell performance interdependently.