CuI/Zn2x(CuIn)1–xS2/AgIn5S8 double heterojunction solar cells



First succesfull attempts to apply ZnS–CuInS2 mixed crystals in double heterojunction p–i–n solar cells in combination with AgIn5S8 and CuI are presented. Besides of studying the optoelectronic properties of the heterojunction structures, a special attention is paid to the problem of optimal band offsets and of the chemical stability. The influence of band offsets on the conversion efficiency was treated by simulation using SCAPS software, whereas the experimental band offsets were measured using X-ray photoelectron spectroscopy. The trend of the open circuit voltage change vs. ZnS concentration can be explained by the observed change of the band offset at the interface with AgIn5S8. For each combination of the n-type and p-type materials in a p–i–n heterostructure, a certain maximum possible band gap in the i-type material exists, still allowing the perfect band alignment. This band gap is about 1.2 eV for AgIn5S8 + CuI combination. The band gaps of all ZnS–CuInS2 materials being larger than 1.5 eV are too large to be used in optimal double heterojunction devices in this system. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)