SOLAR CELL, MULTI-JUNCTION SOLAR CELL, SOLAR CELL MODULE, AND SOLAR POWER GENERATION SYSTEM

Solution to Problem of the present invention provides a solar cell, a solar cell module, and a photovoltaic power generation system having excellent. A solar cell according to an embodiment includes a p-electrode, a p-type light-absorbing layer containing a cuprous oxide or/and a complex oxide of cuprous oxides as a main component on the p-electrode, an n-type layer containing an oxide containing Ga on the p-type light-absorbing layer, and an n-electrode. A first region is included between the p-type light-absorbing layer and the n-type layer. The first region is a region from a depth of 2 nm from an interface between the p-type light-absorbing layer and the n-type layer toward the p-type light absorbing layer to a depth of 2 nm from the interface between the p-type light-absorbing layer and the n-type layer toward the n-type layer. Cu, Ga, M1, and O are contained in the first region. M1 is one or more elements selected from the group consisting of Sn, Sb, Ag, Li, Na, K, Cs, Rb, Al, In, Zn, Mg, Si, Ge, N, B, Ti, Hf, Zr, and Ca. A ratio of Cu, Ga, M1, and O is a1 : b1 : c1 : d1. a1, b1, c1, and d1 satisfy 1.80 ≤ a1 ≤ 2.20, 0.005 ≤ b1 ≤ 0.05, 0 ≤ c1 ≤ 0.20, and 0.60 ≤ d1 ≤ 1.00.