Efficiency enhancement using a Zn₁− xGex-O thin film as an n-type window layer in Cu₂O-based heterojunction solar cells

Efficiency enhancement was achieved in Cu 2 O-based heterojunction solar cells fabricated with a zinc–germanium-oxide (Zn 1− x Ge x -O) thin film as the n-type window layer and a p-type Na-doped Cu 2 O (Cu 2 O:Na) sheet prepared by thermally oxidizing Cu sheets. The Ge content ( x ) dependence of the obtained photovoltaic properties of the heterojunction solar cells is mainly explained by the conduction band discontinuity that results from the electron affinity difference between Zn 1− x Ge x -O and Cu 2 O:Na. The optimal value of x in Zn 1− x Ge x -O thin films prepared by pulsed laser deposition was observed to be 0.62. An efficiency of 8.1% was obtained in a MgF 2 /Al-doped ZnO/Zn 0.38 Ge 0.62 -O/Cu 2 O:Na heterojunction solar cell.