Shinku

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Cu/CdS thin-film photovoltaic cells were fabricated by vacuum deposition. The CdS thin films deposited on the SnO₂-coated glass substrate were annealed with the CdS (Cu, Cl) powder at 400-430°C, and were etched lightly using 10% HNO₃. The Cu thin films were deposited on the CdS films as the counter-electrode and the dopant. The Cu/CdS thin-film cells were heat treated at 400-450°C for 7-10 min. This heat treatment effectively improved the photovoltaic characteristics of the Cu/CdS thin-film cells. The spectral response of the short-circuit current (I_sc) to the illumination through the Cu electrode was larger at short wavelengths than the absorption edge of the CdS and decreased sharply near the absorption edge, but the response to the illumination through the SnO₂ electrode did not appear at short wavelengths but was observed at long wavelengths. If the Cu₂S layer contributes to the photovoltaic effect of the cells, then the spectral response of I_sc does not decrease sharply near the absorption edge of CdS, because the spectral characteristics of the absorption coefficient of Cu₂S differ from those of the CdS. Therefore, we concluded that the photovoltaic effects of Cu/CdS thin-film cells are not caused by the Cu₂S/CdS heterojunction, but by the i-n homojunction of CdS.

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