Thin-film silicon solar cells using back reflector with embedded metal nanoparticles

Light trapping in the absorber layer of thin-film solar cells is of great importance for obtaining a high photocurrent. A novel light-trapping technique is based on light scattering by metal nanoparticles through excitation of localized surface plasmons. By evaporation of thin silver layers of different thicknesses followed by thermal annealing, silver nanoparticles with different sizes were formed. We show that the plasmon resonance wavelength can be tuned by changing the embedding medium and the particle size. Furthermore, amorphous silicon solar cells with silver nanoparticles embedded between the absorber layer and the back reflector were fabricated. The effect of different sizes of the particles on the solar cell performance was studied. The performance of the solar cells was characterized by quantum efficiency and current-voltage measurements. Both the external quantum efficiency in the wavelength region of 600 to 800 nm and the current density increase as particle size increases, but remain lower than those of the reference device without particles. These results demonstrate that nanoparticles can enhance light trapping, provided that parasitic absorption in the nanoparticles is minimized. This can be achieved by better control of particle shape and size using improved fabrication techniques.