According to the optical electromagnetic theory, this paper demonstrates that we should not apply the usual simplified theoretical formulas of transparent dielectric (such as glass) to design semiconductor (Si) cell antireflection (AR) films. We must consider the macroscopic optical properties of semiconductor itself. We have deduced a strict formula for wide band three-layer AR coatings on semiconductor (Si) cell. By this formula, we can calculate the 'theoretical reflectance' of solar cells at any film thickness and wavelength. We have screened some type of double-layer film that increased the current gain of space solar cell effectively. For outerspace solar cells, it is necessary to have an 'optical matching system,' which is made up several layers of transparent material: AR coatings of silicon, silicon rubber adhesive and anti-radiation cover glass. For the solar cell with 'optical matching system,' we have also formulated its total reflectance Rt as a function of the reflectance Rm from AR film upon silicon, the index of refraction of cover glass ng, the index of refraction of silicon rubber adhesive nj, the transmittance of the upper surface of glass T.Rt has a parabolic type of T.