Plasmonic light-trapping and quantum efficiency measurements on nanocrystalline silicon solar cells and silicon-on-insulator devices

Quantum efficiency measurements in nanocrystalline silicon (nc-Si:H)solar cells deposited onto textured substrates indicate that these cells are close to the "stochastic light-trapping limit" proposed by Yablonovitch in the 1980s. An interesting alternative to texturing is "plasmonic" light-trapping based on non-textured cells and using an overlayer of metallic nanoparticles to produce light-trapping. While this type of light-trapping has not yet been demonstrated for nc-Si:H solar cells, significant photocurrent enhancements have been reported on silicon-on-insulator devices with similar optical properties to nc-Si:H. Here we report our measurements of quantum efficiencies in nc-Si:H solar cells and normalized photoconductance spectra in SOI photodetectors with and without silver nanoparticle layers. As was done previously, the silver nanoparticles were created by thermal annealing of evaporated silver thin films. We observed enhancement in the normalized photoconductance spectra of SOI photodetectors at longer wavelengths with the silver nanoparticles. For nc-Si:H solar cells, we have not yet observed significant improvement of the quantum efficiency with the addition of annealed silver films.