Disclosed is a method of forming a chalcopyrite light-absorbing layer for a solar cell, including: forming a thin film including a chalcopyrite compound precursor; and radiating light on the thin film, wherein the chalcopyrite compound precursor absorbs light energy and is thus crystallized. When forming the chalcopyrite light-absorbing layer, light, but not heat, is applied, thus preventing problems, including damage to a substrate due to heat and formation of MoSe2 due to heating of the Mo rear electrode. Furthermore, long-wavelength light, which deeply penetrates the thin film, is first radiated, and short-wavelength light, which shallowly penetrates the thin film, is subsequently radiated, thereby sequentially forming the chalcopyrite light-absorbing layer from the bottom of the thin film.