Photovoltaic Properties in Al-doped ZnO/non-doped Zn1-XMgXO/Cu2O Heterojunction Solar Cells

The influence of Mg content (Mg/(Mg+Zn) atomic ratio) on the obtainable photovoltaic properties in Al-doped ZnO (AZO)/non-doped Zn1-XMgXO/Cu2O heterojunction solar cells using p-type Cu2O sheets prepared by thermally oxidizing Cu sheets was investigated. n-type Zn1-XMgXO thin films were prepared with various Mg contents on non-intentionally heated Cu2O sheets using a pulsed laser deposition. It was found that the obtained open circuit voltage increased gradually as the Mg content was increased up to approximately 0.18. The optimal Mg content in the n-Zn1-XMgXO thin-film layer that would be suitable for achieving the highest efficiency was determined to be approximately 0.09. The obtained short circuit current density, fill factor and conversion efficiency increased gradually as the O2 gas pressure during the depositions was increased, reaching maximum values at a pressure of approximately 1 Pa, and then their values decreased as the pressure was increased further. In contrast, the open circuit voltage increased monotonically from 0.62 to 0.85 V as the O2 gas pressure was increased from vacuum (below 4×10-4 Pa) to 1.6 Pa. The highest efficiency of 4.31%, measured under AM1.5G (100 mW/cm2) solar illumination, was obtained in an AZO/Zn0.91Mg0.09O/Cu2O heterojunction solar cell fabricated with an n-Zn0.91Mg0.09O thin-film layer prepared with a thickness of 50 nm at an O2 gas pressure of 0.9 Pa.