Optical design and fabrication of fully sputtered CdTe/CdS solar cells

Abstract

A model is presented for optimising the integrated intensity of light passing into the absorber layers of thin-film solar cells. Dispersion data for each of the transparent layers in the cells was obtained from variable angle spectroscopic ellipsometry. This data was then used in a transfer matrix model of multi-layer optics to determine the intensity spectrum passing over the interface from the transparent to the absorbing parts of the cell. Application of the method to the case of CdTe/CdS/ZnO/ITO/glass solar cells is described in detail, including the fitting of oscillator models to extract the complex dielectric function from the ellipsometry data. It was found that light coupling into the absorber was particularly sensitive to the CdS thickness but that tuning the ZnO (highly resistive transparent) layer was also influential. All-sputtered cells of this type were demonstrated as having efficiencies of 12.5% for 5 × 5 mm2 contacts. © Published under licence by IOP Publishing Ltd 2011.