Evidence for CdTe1−xSx compound formation in CdTe solar cells from high-precision, temperature-dependent device measurements

High-precision, temperature-dependent device measurements have been made on CdTe solar cells fabricated by close-spaced sublimation on CdS-coated SnO₂:F-glass substrates. In particular, the temperature dependence of V_oc was measured from 110 K-310 K, taking care that the wavelengths of the incident light did not overlap the absorber band edge. The conventional deduction of the absorber bandgap E_g was clarified by taking into account its temperature dependence. Depending upon fabrication conditions, it was found that the 0 K extrapolated bandgap of the region of the absorber in which most recombination occurs was 1.33 e V, i.e. significantly less than that of CdTe. It was concluded that this region consists of the compound CdTe_1-xS_x.