The invention is a method of forming a cadmium sulfide based buffer on a copper chalcogenide based absorber in making a photovoltaic cell. The buffer is sputtered in two steps the first being at low rates or relatively high pressures and the second at high rates or relatively low pressures. The resulting cell has good efficiency and according to one embodiment is characterized by a narrow interface between the absorber and buffer layers. The buffer is further characterized according to a second embodiment by a relatively high oxygen content.