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

A solar cell of an embodiment includes a p-electrode, an n-electrode, a p-type light-absorbing layer located between the p-electrode and the n-electrode and comprising a cuprous oxide, and an n-type layer comprising a first n-type layer, which is located between the p-type light-absorbing layer and the n-electrode and comprising a defined compound aiding in conversion efficiency. The n-type layer further comprises a second n-type layer which is located between the first n-type layer and the n-electrode and mainly contains another compound aiding in conversion efficiency.