Resonant enhancement of metal nanoparticle arrays fabricated with nanoimprint lithography

Plasmonic effects on metal particles are a promising way of trapping light in solar cells. We experimentally demonstrate enhanced absorptance in thin silicon using metal nanoparticle arrays in conjunction with a rear mirror. The nanoimprint process is a fast and scaleable method for producing nanoscale light trapping structures. Incorporating both nanoparticle arrays and a rear mirror leads to a substantial increase in absorptance, due to resonant interference effects. We numerically simulate a planar Ag mirror deposited onto a planarized sol-gel silicon dioxide (SiO2) layer, and show the enhancement could reach 53%. We also find that a conformal Ag mirror deposited on a sputtered SiO2 layer could give similar enhancement. Experimentally, we derive predicted Jsc enhancements of up to 2.8 mA/cm2 from absorptance measurements. The experimental results show good qualitative agreement with numerical simulations as the thickness is increased, with clear evidence of absorptance enhancement via a Fabry-Perot resonance effect

Light trapping with titanium dioxide diffraction gratings fabricated by nanoimprinting

Dielectric scattering structures are a promising way of trapping light in solar cells. Titanium dioxide is a particularly attractive candidate material because of its high refractive index and ability to be deposited on a finished solar cell. Here, we present an experimental demonstration of photocurrent enhancement in thin film recrystallised silicon solar cells using TiO2 pillar arrays fabricated on the rear of the cells using nanoimprint lithography. A short circuit current enhancement of 19% is measured experimentally, and excellent agreement with numerical simulations is obtained. We show numerically that by replacing the Ag capping present on the cells with a detached rear Ag back reflector, the enhancement could reach 37%