CdS enhances V_(oc) and fill factor in CdS/CdTe and CdS/CulnSe_2 solar cells

摘要

A cover layer of CdS enhances the efficiency of CdTe and CuInSe_2 based solar cells. The experimental results are summarized, giving the reasons why a CdS layer causes V_(oc) and the fill factor to increase. Field quenching by Frenkel-Poole excitation in copper doped CdS leads to a negative differential conductivity and a high-field domain with a field of 50 kV/cm, limiting the maximum field in the CdS/CdTe junction. This prevents tunneling through the junction and reducing electron leakage. Other evidence indicates an adjustment of the electron affinity, hence in a shift of the band connection at different bias conditions. A band model of the CdS/CdTe cell is proposed.