NOVELTY - The solar cell i.e. copper indium gallium selenide (CIGS)-based thin film solar cell (100), has a p-type semiconductor CIGS based optical absorption layer (140) provided on a hole injection layer (130), where a difference between a valence band of the injection layer and a valence band of the absorption layer is larger than a difference between a conduction band of the injection layer and the valence band of the absorption layer. An anti-reflective layer (170) is provided at a portion of region on a front transparent electrode (160) that is provided on the absorption layer.    USE - Compound semiconductor solar cell i.e. CIGS-based thin film solar cell.    ADVANTAGE - The thickness of the injection layer is about 0.001 micrometer to about 1.0 micrometer, thus improving performance of the solar cell. The anti-reflective layer is formed at the portion of region on the front transparent electrode, so as to reduce a reflective loss of solar light incident on the solar cell, thus improving the efficiency of the solar cell. The solar cell utilizes a sodalime glass substrate that is made of low cost substrate material, where sodium in the substrate diffuses into the optical absorption layer, thus improving photovoltaic characteristics of the solar cell. The back electrode of the solar cell has low resistivity and excellent adhesion to the substrate, such that an exfoliation phenomenon does not occur due to the difference in thermal expansion coefficients. The front transparent electrode is formed at a front face of the solar cell to function as a window, and is formed of a material that has a high optical transmittance and good electrical conductivity.    DETAILED DESCRIPTION - The injection layer is formed with a thickness of about 0.001 micrometer to about 1.0 micrometer. The absorption layer comprises I-III-VI2 group compound semiconductors. The electrode is made of a stacked layer of an n-type zinc oxide thin film.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of a CIGS based thin film solar cell.    CIGS-based thin film solar cell (100)    Hole injection layer (130)    P-type semiconductor CIGS based optical absorption layer (140)    Front transparent electrode (160)    Anti-reflective layer (170)