The effects of the band bending caused by interface states in CdTe/CIS solar cells

In this paper, the effects of interface states in ZnO/CdS/CuInSe ₂ and CdS/CdTe solar cells are presented. The effects are investigated through numerical modeling using the ADEPT (A Device Emulation Program and Tool) software package. The results show that donor-like interface states have very little effect, but acceptor-like interface states at the resistive ZnO/CdS can cause pinning of the bands at the interface, thus leading to nonexponential illuminated I-V curves when the interface state densities are high enough. High density of acceptor-like states between the CdS and In-rich CIS does not result in the two-diode like IV curves. Instead they can significantly lower the fill factor. In the CdS/CdTe solar cells, either donor- or acceptor-like interface states have little effect since almost all the depletion region lies in the CdTe. Thus, the metallurgical junction where the interface states are located is away from the electrical junction where the conductivity type changes