Doping and intermixing in CdS/CdTe solar cells fabricated under different conditions

Thin film CdS/CdTe solar cell structures have been investigated by spatially resolved cathodoluminescence (CL) spectroscopy. A postgrowth ${\mathrm{CdCl}}_{\mathrm{2}}$ treatment of the CdTe layer was found to homogenize the distribution of acceptor-like defects or impurities leading to optimized p-type conversion of the polycrystalline CdTe. For values of the growth temperature ${\mathrm{(T}}_G)$ of about 600 °C, the intermixed region between the CdS layer and CdTe grains is surprisingly thin. However, for $T_G$ as large as 630–650 °C, a gradual decrease of the CdTe band gap due to sulfur intermixing appears to be present up to 0.6 μm from the CdS/CdTe interface. The CL spectra of the CdS window layer exhibit two broad bands centered at 1.72 (red) and 2.04 eV (yellow). The yellow one is quenched by the ${\mathrm{CdCl}}_{\mathrm{2}}$ treatment, indicating passivation or promoted outdiffusion of Cd interstitials.