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, comprising steps of:

• providing a substrate;
• forming a back electrode layer on the substrate;
• forming sequentially a first metal layer, a second metal layer, and a third metal layer on the back electrode layer, wherein the first metal layer, the second metal layer, and the third metal layer are a group III element, a group I element, and a group III element, respectively;
• providing a group VI element and a reaction process for allowing the first metal layer, the second metal layer, the third metal layer, and the group VI element to form a light-absorbing layer of a I-III-VI compound, wherein the light-absorbing layer has a band gradient, the group III elements comprise indium (In) and aluminum (Al), and an aluminum to indium (Al/In) ratio in an upper half portion of the light-absorbing layer is greater than that in a lower half portion of the light-absorbing layer, the upper half portion being proximate to a light incident surface;
• forming a buffer layer on the light-absorbing layer;
• forming a window layer on the buffer layer;
• and
• forming a top electrode layer.