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)Se2 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)Se2/Sb2S3/ZnO solar cells have been investigated. While the open circuit voltage ranged up to ∼0.4–0.5 V, the short circuit current was limited to ∼1.8–4.9 mA/cm2. A photocurrent of about 30 mA/cm2 was found for negative bias. On the basis of bias dependent quantum efficiency measurements and calculations, limiting mechanisms are discussed.