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

Deposition of Cd x Zn 1−x O y S 1−y was demonstrated with atomic layer deposition (ALD) using diethylzinc (DEZn), dimethylcadmium (DMCd), H 2 O, and H 2 S 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 CuInS 2 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 x Zn 1−x O y S 1−y system leads to increases in the J SC due to decreased parasitic absorption from the increase in bandgap due to Zn.