NOVELTY - Manufacture of complex and its solution involves obtaining a reaction solution by mixing one or more simple substance or compound chosen from group 11 metal, group 12 metal, group 13 metal, group 14 metal, group 15 element, group 11 metal compound, group 12 metal compound, group 13 metal compound, group 14 metal compound and group 15 element-containing compound, one or more chalcogen element-containing organic compound chosen from mercapto group-containing organic compound and selenium-containing heterocyclic compound, Lewis base inorganic compound and group 16 element.    USE - Manufacture of complex and its solution used for manufacturing light absorption layer for manufacturing solar cell e.g. chalcopyrite-type solar cell and kesterite-type solar cell (all claimed).    ADVANTAGE - The light absorption layer is economically manufactured using the complex and its solution, with reduced usage amount of organic substance used as factor which inhibits crystal growth. The solar cell manufactured using the light absorption layer has excellent photoelectric conversion efficiency.    DETAILED DESCRIPTION - Manufacture of complex and its solution involves obtaining a reaction solution by mixing one or more types of simple substance or compound chosen from group 11 metal, group 12 metal, group 13 metal, group 14 metal, group 15 element, group 11 metal compound, group 12 metal compound, group 13 metal compound, group 14 metal compound and group 15 element-containing compound, one or more chalcogen element-containing organic compound chosen from mercapto group-containing organic compound, sulfide, polysulfide, thiocarbonyl group-containing organic compound, sulfur-containing heterocyclic compound, hydroseleno group-containing organic compound, selenide, polyselenide, selenocarbonyl group-containing organic compound and selenium-containing heterocyclic compound, Lewis base inorganic compound and group 16 element. INDEPENDENT CLAIMS are included for the following:    (1) manufacture of light absorption layer (4); and    (2) manufacture of solar cell.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of chalcopyrite-type solar cell or kesterite-type solar cell.    Substrate (2)    Electrodes (3,7)    Light absorption layer (4)    Buffer layer (5)    Antireflective film layer (8)