Thin-film junctions of cadmium telluride by metalorganic chemical vapor deposition

Polycrystalline films of cadmium telluride (CdTe) deposited by the metalorganic chemical vapor deposition (MOCVD) technique using the reaction of dimethylcadmium (DMCd) and di-isopropyltellurium (DIPTe) can be p type or n type, depending on the DMCd/DIPTe molar ratio in the reaction mixture. Extrinsic CdTe films have been deposited by using group III and group V compounds as dopants during the MOCVD process. Gallium can be incorporated into CdTe films to yield a dark resistivity of about 1000 Ω cm and a carrier concentration of about 2×1017 cm−3; however, the incorporation of arsenic or antimony is considerably more difficult, and low resistivity p-CdTe films cannot be obtained. Extrinsically doped CdTe films show significantly different photoluminescence spectra from intrinsic films of the same conducting type. Heterojunctions have been prepared by depositing p-CdTe films on CdS-coated SnO2:F/glass substrates. The junction properties and the post-deposition treatments have been investigated. Large-area (≳1 cm2) MOCVD CdTe thin-film solar cells of near 10% efficiency have been reported for the first time. Homojunctions have also been prepared by the successive in situ deposition of n- and p-CdTe films on SnO2:F/glass substrates, and their photovoltaic characteristics evaluated.