This invention provides a CIS-based thin film
solar battery and a process for producing the same in which the formation of an alkali
barrier layer and a
metal backside
electrode layer is carried out at a low cost in a short time to prevent such an unfavorable phenomenon that a light absorbing layer is separated from the interface of the light absorbing layer and the
metal backside
electrode layer. The CIS-based thin film
solar battery (1) comprises a glass substrate (2), an alkali-free layer (7) such as silica, a
metal backside
electrode layer (3) having a laminate structure, a p-type CIS-based light absorbing layer (4), a high-resistance buffer layer (5), and an n-type window layer (6) stacked in that order. The layer (7), either alone or together with a first layer (3a) in the layer (3), can function as an alkali
barrier layer (8) that can prevent and control the thermal
diffusion of an alkali component into the light absorbing layer during the formation of the layer (4) from the substrate (2). In the layer (3a),
crystal grains are fine and has
high density. After the formation of the layer (7) on the substrate by RF or DC
sputtering, the layer (3) is continuously formed on the layer (7) by DC
sputtering.