X-ray photoemission analysis of CS2 treated polycrystalline Cu(In,Ga)Se2

Abstract Device-grade polycrystalline thin-film Cu(In 0.5 Ga 0.5 )Se 2 was treated with CS 2 to determine the resulting microscopic surface composition/morphology. Scanning electron microscopy (SEM) was used to evaluate the resultant surface morphology. Angle-integrated high-resolution photoemission measurements on the valence band (Cu 3d) electronic structure and In 4d/Ga 3d, Se 3d and S 2p core lines were used to evaluate the chemistry of the CS 2 treated surface. Results show that the surface has been planarized by the highly reactive CS 2 treatment and that S has been incorporated at the surface, possibly creating a wider bandgap Cu(In 1− x Ga x )(Se 1− y S y ) 2 surface layer. The purpose of this investigation is to find an environmentally safe replacement for the toxic CdS overlayer commonly used for heterojunction devices without sacrificing overall device performance and reliability.