Enhanced quantum efficiency of Ge solar cells by a two-dimensional photonic crystal nanostructured surface

3 pages, 5 figures.-- PACS: 84.60.Jt; 42.70.QsA single-junction germanium solar cell with a photonic crystal nanostructured surface has been developed. The solar cell comprises a Ge p-n junction and an InGaP window layer. The InGaP window layer has been nanopatterned with an extended photonic crystal structure consisting on a triangular lattice of holes with submicronic sizes. Enhancements of the external quantum efficiency of 22% for a wide range of wavelengths and up to a 46% for specific wavelengths have been measured, which implies an increase in photocurrent between 11% and 22%. A clear correlation with the area of photonic crystal patterned has been observed.The authors would like to acknowledge support from projects NAN2004-08843-C05-04, NAN2004-09109-C04- 01, TEC-2005-05781-C03-01, CONSOLIDER-Ingenio 2010 “Genesis-FV” project (Project No. CSD2006004 ), TEC200502745. TEC200422300E, NUMANCIA (Grant No. S05050/ENE/0310).Peer reviewe