Solar cell, multi-junction solar cell, solar cell module, and solar power generation system

A solar cell comprising:

• a substrate;
• a first transparent electrode;
• a second transparent electrode;
• a p-type photoelectric conversion layer containing cuprous oxide disposed between the first transparent electrode and the second transparent electrode;
• an n-type layer disposed between the p-type photoelectric conversion layer and the second transparent electrode, wherein
• the p-type photoelectric conversion layer has a thickness of 500 nm or more and 0.3 mm or less,
• at a temperature of 100 K or lower, the p-type photoelectric conversion layer has a photoluminescence spectrum exhibiting a first maximum value (A) which is a maximum value of emission intensity in a wavelength range of more than 650 nm and 1000 nm or less and that is 100 times or less of a second maximum value (B) which is a maximum value of emission intensity in a wavelength range of 600 nm or more and 650 nm or less (A≤100B), and wherein
• the p-type photoelectric conversion layer as analyzed by X-ray photoelectron spectroscopy,
• in a peak of the cuprous oxide observed in a range in which a binding energy value is 930 eV or more and 934 eV or less,
• exhibits a first intersection and a second intersection where a horizontal line passing through a value of ⅔ of a peak top of the cuprous oxide intersects with the peak of the cuprous oxide, and
• exhibits a third intersection where a perpendicular line extending from the peak top to the horizontal line intersects with the horizontal line, wherein
• an average of ratios of a difference between a first length formed by the first intersection and the third intersection and a second length formed by the second intersection and the third intersection is 15% or less,
• the first electrode is formed over the substrate, and
• the p-type photoelectric conversion layer is formed over the first electrode.