Enhanced efficiency of ultrathin (∼500 nm)-film microcrystalline silicon photonic crystal solar cells

Enhancing the absorption of thin-film microcrystalline silicon solar cells at 600–1000 nm wavelengths is very important to the improvement of the energy conversion efficiency. This can be achieved by creating a large number of resonant modes utilizing two-dimensional photonic crystal band edges, which exceeds the Lambertian limit of absorption in random textures. We focus on suppressing the parasitic absorption of back-reflector metal and doped layers in photonic crystal microcrystalline silicon solar cells. We achieve a high active-area current density of 22.6 mA cm−2 for an ultrathin (∼500 nm)-film silicon layer and obtain an active-area efficiency of ∼9.1%, as independently confirmed by the CSMT of AIST.