Photovoltaic device and method for making the same

A method for making a photovoltaic device, comprising:

• providing a first sputtering target of a first chalcopyrite-type compound comprising M1, M2, and A1, in which M1 is selected from Cu, Au, Ag, Na, Li, K and combinations thereof, M2 is selected from In, Ga, Al, Ti, Zn, Cd, Sn, Mg and combinations thereof, and A1 is selected from S, Se, Te and combinations thereof;
• providing a second sputtering target of a second chalcopyrite-type compound comprising M3, M4, and A2, in which M3 is selected from Cu, Au, Ag, Na, Li, K and combinations thereof, M4 is selected from In, Ga, Al, Ti, Zn, Cd, Sn, Mg and combinations thereof, and A2 is selected from S, Se, Te and combinations thereof;
• forming a p-type semiconductor layer on a back electrode by sputtering the first sputtering target such that the p-type semiconductor layer thus formed is made of a first semiconductor compound comprising M1, M2, and A1 and has a substantially uniform M1/M2 atomic ratio throughout an entire layer thickness thereof;
• forming an n-type semiconductor layer on the p-type semiconductor layer by sputtering the second sputtering target such that the n-type semiconductor layer thus formed is made of a second semiconductor compound comprising M3, M4, and A2 and has a substantially uniform M3/M4 atomic ratio throughout an entire layer thickness thereof, the M3/M4 atomic ratio being less than the M1/M2 atomic ratio;
• forming a buffer layer on the n-type semiconductor layer;
• and
• forming a window layer on the buffer layer.