Method of manufacturing stacked-layered thin film solar cell with a light-absorbing layer having band gradient

A method of manufacturing a stacked-layered thin film solar cell with a light-absorbing layer having a band gradient is provided. The stacked-layered thin film solar cell includes a substrate, a back electrode layer, a light-absorbing layer, a buffer layer, a window layer, and a top electrode layer stacked up sequentially. The light-absorbing layer has a band gradient structure and is essentially a group I-III-VI compound, wherein the group III elements at least include indium (In) and aluminum (Al). Moreover, the Al/In ratio in the upper half portion of the light-absorbing layer is greater than that in the lower half portion of the light-absorbing layer, wherein the upper half portion is proximate to a light incident surface.