The Electronic Effects of Cd on the Formation of the Cds/cuins2 Heterojunction

The possibility of doping and Fermi Level pinning of CuInS2 thin layer solar cell absorbers caused by the diffusion of Cd into the absorber during junction formation via chemical bath deposition was investigated. The analysis of thin CdS layers deposited on CuInS2 showed the amount of deposition-induced band bending on the CuInS2 surface (position of the Fermi Level in the respective band gaps) was not experimentally reproducible. However, the value of the valence band offset between the two materials was reproducible between different depositions within the error of the measurement. Thus, the deposition of the CdS does not lead to a consistent pinning position of the Fermi Level in the CuInS2/CdS heterojunction. The removal of the CdS layers with HCl left a thin Cd-containing layer on the CuInS2 surface and it was shown that this surface was not doped by the remaining Cd. Furthermore, the influence of the HCl of the CuInS2 was explored and found to form a reproducible surface richer in Cu than CuInS2 etched in potassium cyanide solution.