Impact of Cu-Au type domains in high current density CuInS₂ solar cells

In this work, a series of stain steel 15×15 cm² CuInS₂ solar cells with efficiencies close to the record one for this kind of devices, are analyzed. Through a careful and comprehensive study of the structural and electronic properties of the CuInS₂ layer, we show that in a general fashion the strain originated by the thermal annealing affects the energy band splitting and reduces the short circuit current. Then, through an innovative combination of photoreflectance and Raman scattering analysis, we demonstrate that the presence of CuAu domains in the bulk layer of a CuInS₂ is directly related with this strain reduction contributing to the improvement of short circuit current. We propose that the presence Cu-Au phase domains reduce the strain within the CuInS₂ layer, and improve the quality of the CIS chalcopyrite crystals, leading to reduced carrier recombination while increasing carriers mobility. As a consequence we conclude that the presence of said domains improves the short circuit current in the studied devices.