Ultra-Thin Organic Solar Cells Incorporating Dielectric-Coated Comb Silver Nanogratings

Although coating engineering on metallic nanostructures has been frequently applied in organic solar cells (OSCs) for improving the device performance by preventing the possible exciton quenching and charge recombination at the metal surface, there have been few theoretical researches addressing how the dielectric-coating of metal nanostructures influences the optical performance of OSCs. Here, we theoretically investigate the effect of coating a comb silver nanograting by a dielectric film on the absorption performance of OSCs. It is found that, under transverse-magnetic (TM) polarization, when the refractive index or thickness of the dielectric-coating is tuned, different orders of plasmonic waveguide modes are excited by the P3HT:PC₆₁BM/coating/Ag triple-layered system. The dispersion relationship of such a plamsonic waveguide mode is solved and analyzed for clarifying the physical mechanism of the induced light trapping effect. It shows that for optimizing the light absorption in active layer under TM polarization, it is more favorable to coat a thin dielectric film (of 1 nm thick) with a suitable refractive index. While under transverse-electric (TE) polarization, the higher refractive index of dielectric-coating, the better the effect of light trapping.