Graded and alloyed II-VI semiconductors for photovoltaic buffer layers grown by atomic layer deposition (ALD)

Deposition of Cd_xZn_1-xO_yS_1-y was demonstrated with atomic layer deposition (ALD) using diethylzinc (DEZn), dimethylcadmium (DMCd), H₂O, and H₂S as the precursors. The chemical, material, and optical properties of the films were investigated, and these properties were adjusted by varying the stoichiometry. Notably, by correlating the crystal phases to the optical constants and bandgap, strong relationships between optical and materials properties are determined. Deposition of buffer layers at 150 °C on CuInS₂ absorbers was demonstrated and characterization of working devices was shown with IV curves and quantum efficiency measurement. CdS ALD buffer films behave similar to CdS chemical bath deposition (CBD) films even when slightly thinner than normal. Depositing mixed films across the Cd_xZn_1-xO_yS_1-y system leads to increases in the J_SC due to decreased parasitic absorption from the increase in bandgap due to Zn.