Disclosed is a method of manufacturing a thin-film light-absorbing layer using spraying, including mixing precursor solutions comprising CuCl2, InCl3 and SeC(NH2)2 under a nitrogen atmosphere at room temperature thus preparing a mixture solution; spraying the mixture solution on a substrate and drying it, thus forming a thin film; and selenizing the thin film under a selenium atmosphere. A method of manufacturing a thin-film solar cell is also provided, which includes forming a back contact layer on a glass substrate using sputtering; forming a light-absorbing layer on the back contact layer using spraying; forming a buffer layer on the light-absorbing layer using chemical vapor deposition; forming a window layer on the buffer layer using sputtering; and forming an upper electrode layer on the window layer.