Impact of incorporating sodium into polycrystalline p-type Cu2O for heterojunction solar cell applications

The resistivity was controlled in the range of 103 to 10−2 Ω cm in polycrystalline p-type Cu2O sheets (incorporating sodium (Na)), which are suitable for Cu2O-based heterojunction solar cell applications. The Na-doped Cu2O sheets exhibited a hole concentration that ranged from 1013 to 1019 cm−3. In particular, a hole concentration of 1013–1016 cm−3 was obtained while maintaining a high Hall mobility above 100 cm2/V s, and, in addition, a degenerated semiconductor exhibiting metallic conduction was realized with a hole concentration above about 1 × 1019 cm−3. The mechanism associated with the Na doping can be explained by a copper vacancy produced due to charge compensation effects that result when a Na atom is incorporated at an interstitial site in the Cu2O lattice. For solar cell applications, the use of the Cu2O:Na sheet in a heterojunction solar cell successfully improved the obtained efficiency over that found in heterojunction solar cells fabricated using an undoped Cu2O sheet.