Si/Si1−xGex nanopillar superlattice solar cell: A novel nanostructured solar cell for overcoming the Shockley-Queisser limit

We propose a novel Si/Si_1-xGe_x nanopillar superlattice solar cell enabling quantum confinement, light trapping, increased lifetime, and efficient carrier extraction for the first time. An average reflectance as low as 3.2% was achieved by adopting a hybrid nanopillar array structure. Auger recombination lifetime was significantly increased from 4×10^-10 s to 2× 10^-8 s by barrier height engineering of the Si/Si_1-xGe_x superlattice. These two techniques are predicted to improve solar cell efficiency from 23% to 35%. Our results demonstrate the possibility of overcoming the theoretical (Shockley-Queisser) limit (30%) of conventional Si solar cell.