A method for manufacturing a thin film type solar cell is disclosed, which is capable of reducing degradation of solar cell by decreasing the number of dangling bonding sites or SiH2 bonding sites existing in amorphous silicon owing to an optimal content ratio of ingredient gases, an optimal chamber pressure, or an optimal substrate temperature during a process for depositing an I-type semiconductor layer of amorphous silicon by a plasma CVD method, the method comprising forming a front electrode layer on a substrate; sequentially depositing P-type, I-type, and N-type semiconductor layers on the front electrode layer; and forming a rear electrode layer on the N-type semiconductor layer, wherein the process for forming the I-type semiconductor layer comprises forming an amorphous silicon layer by the plasma CVD method under such circumstances that at least one of the aforementioned conditions is satisfied, for example, a content ratio of silicon-containing gas to hydrogen-containing gas is within a range between 1:7 and 1:10; a chamber pressure is maintained at a range between 2.0 Torr and 2.4 Torr; and a substrate temperature is maintained at a range between 225° C. and 250° C.