The invention discloses a GaAs unijunction solar cell. An electrode and a double-layer antireflection film are formed on the surface of an epitaxial layer of the cell; and an upper film of the double-layer antireflection film is made of a material with a refractive index smaller than that of a lower film, while the lower film is made of a photoluminescence material with a refractive index betweenthe refractive indexes of the upper film and a window layer. The photoluminescence material can absorb the sunlight of a wave band which cannot be absorbed by GaAs and convert the part of sunlight into light which can be absorbed by the GaAs so that the sunlight of the wider wave band is absorbed by the GaAs solar cell and converted into electrical energy, the absorption wave band of the GaAs unijunction solar cell on the sunlight is greatly broadened and the photoelectric conversion efficiency of the cell is improved.