Application of Mapping Spectroscopic Ellipsometry for CdSe/CdTe Solar Cells: Optimization of Low-Temperature Processed Devices with All-Sputtered Semiconductors

The incorporation of CdSe as a top component layer in superstrate CdTe photovoltaics (PV) technology has led to improvements in short-circuit current due to collection at both violet and near-infrared edges of the external quantum efficiency spectra. The achievable improvements are very sensitive to the details of device fabrication including the individual CdSe and CdTe layer thicknesses and the thermal profile of the entire process. In this research, mapping spectroscopic ellipsometry (M-SE) is being applied at different stages of the process, in conjunction with previously-established capabilities of through-the-glass SE (TG-SE) and variable-angle SE (VA-SE), all toward the development of an advanced metrology for this new absorber layer alloy system. In this report, correlations are presented between the effective thickness (or volume/area) of thin film CdSe, obtained by M-SE prior to CdTe deposition, and the ultimate device performance.