TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Method: The method further comprises forming a buffer layer (60) between the light absorption layer and the second electrode. In the method, the precursor is formed so that composition ratio of copper/(gallium+indium) is 1 or more. The forming of the light absorption layer includes: controlling the composition ratio of copper/(gallium+indium) in the light absorption layer to be 1 or less by providing the compound that includes gallium (preferred) or indium by using a chemical vapor deposition method; forming a copper, indium, gallium, selenium (CIGS) compound by reacting the compound with the copper-selenium compound; heat treatment; and providing selenium. The forming of the light absorption layer forms the light absorption layer in which an energy band profile has a double graded band-gap structure by providing the compound by using a chemical vapor deposition method. The forming of the preliminary light absorption layer includes: forming the CIGS compound, and the copper-selenium compound in liquid phase; heat treatment; and providing selenium to the precursor while performing heat treatment. The forming of the precursor includes: forming the first layer that includes a copper-gallium compound or a copper-indium compound on the first electrode; and forming a second layer that includes gallium or indium on the first layer, where the forming of the first layer and the forming of the second layer use a sputtering method. Preferred Components: The light absorption layer is disposed in a first region that is close to the first electrode, a second region that is close to the second electrode, and a third region that is disposed between the first region and the second region. The double graded bandgap structure is formed so that the bandgap in the first region and the second region is larger than the bandgap in the third region. The compound is a compound that includes gallium, including trimethyl gallium. The first electrode is formed of a reflective metal. The second electrode is formed of a transparent conductive material. EXAMPLE - No suitable example given.