Band alignment at Sb2S3/Cu(In,Ga)Se2 heterojunctions and electronic characteristics of solar cell devices based on them

Band offsets at Sb2S3/Cu(In,Ga)Se-2 heterojunctions have been studied by x-ray and ultraviolet photoemission spectroscopy. The valence and conduction band offset have been estimated to -(0.6 +/- 0.3) eV and (0.2 +/- 0.3) eV, respectively. This result suggests Sb2S3 as a potential buffer layer material for chalcopyrite based solar cells. However, Cu(In,Ga)Se-2/Sb2S3/ZnO solar cells have been investigated. While the open circuit voltage ranged up to similar to 0.4-0.5 V, the short circuit current was limited to similar to 1.8-4.9 mA/cm(2). A photocurrent of about 30 mA/cm(2) was found for negative bias. On the basis of bias dependent quantum efficiency measurements and calculations, limiting mechanisms are discussed. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3457439]