TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The first solid material layer is provided on the second solid material layer, and a first electrode (7) is provided on a sunlight-receiving surface on the first solid material layer. The solar cell further comprises a second electrode provided on a side of the second solid material layer, where the side is opposite to a side on which the second solid material layer is in contact with the first solid material layer. In the solar cell, at least two of the p-n junction structures each formed of the first solid material layer and the second solid material layer are provided, and the p-n junction structures are connected in series. A light-receiving surface of the solar cell has an irregular surface structure. The Mott insulator or the Mott semiconductor contains at least one transition metal element comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, niobium, molybdenum, ruthenium, rhodium, cadmium, indium, tin, tantalum, tungsten, rhenium, osmium, iridium, or platinum. The Mott insulator or the Mott semiconductor is an inorganic compound comprising metal complex of formula (LnxA(1-x)B1O3) (I), (LnAB12O6) (II), (Ln(1-x)A(1+x)B1O4) (III), (Ln(2-2x)A(1+2x)B12O7) (IV), (Ln(2-x)AxB1O4) (V), (A2B1O3) (VI), (A2B1O4) (VII) or (A2B1O2Cl2) (VIII). The Mott insulator or the Mott semiconductor is vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, or rhenium oxide.Ln = rare-earth elements comprising La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu;A = alkaline earth metal elements comprising Be, Mg, Ca, Sr or Ba;B1 = transition metal elements comprising Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ru, Rh, Cd, In, Sn, Ta, W, Re, Os, Ir or Pt; andx = 0-1.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The Mott insulator or the Mott semiconductor is at least one organic compound comprising aromatic amine compounds, carbazole derivatives, aromatic hydrocarbons, polymer compounds, or charge transfer complexes, where the charge transfer complex is a quasi-one dimensional halogen-bridged metal complex, where a transition metal and a halogen are alternately arranged, a quasi-one-dimensional halogen-bridged multinuclear metal complex, and a quasi-one-dimensional charge transfer complex including tetrathiafulvalene and chloranil.