A method for manufacturing a thin film solar cell includes depositing a front electrode on a substrate in a chamber, etching the front electrode formed on the substrate to form an uneven portion on the surface of the front electrode, forming a photoelectric conversion unit on the front electrode, and forming a back electrode on the photoelectric conversion unit. The depositing of the front electrode includes depositing the front electrode while reducing a process pressure of the chamber from a first pressure to a second pressure lower than the first pressure. The etching of the front electrode form the uneven portion of the front electrode so that a top portion of the uneven portion includes a portion formed at the second pressure.