Transparent Cu2O solar cell for high-efficiency and low-cost tandem photovoltaics

Transparent Cu
₂
O thin film solar cells were fabricated using reactive sputtering of Cu in oxygen atmosphere for use in tandem cells. High transparency and power generation of Cu
₂
O thin film solar cells were confirmed for the first time in the world. Prototype four-probe tandem Cu
₂
O/Si cells were fabricated to confirm the power generation of the Si bottom cell. The infrared transmittance of the Cu
₂
O top cell was high enough that the Si bottom cell generated almost 80% of its maximum power output.