Optimization of ZnO films for the development of ZnO/NiO heterojunction solar cells

This study explores the fabrication and analysis of ZnO/NiO junctions and the electrical properties of Al-doped ZnO (AZO) films. ZnO/NiO junctions were prepared using reactive co-sputtering in an Ar–O2 atmosphere, while AZO films were grown via RF magnetron sputtering at substrate temperatures (TS) ranging from 50 to 400 °C. The visible transmission of AZO films varied significantly, from 2 to 85%, across this temperature range. Films deposited at lower temperatures (~ 50 °C) exhibited pronounced non-stoichiometry, whereas those at higher temperatures (~ 400 °C) were stoichiometric. Nickel oxide films grown at room temperature (RT) achieved exceptional transmittance exceeding 80%, while RT-deposited AZO films demonstrated degenerate properties with a carrier concentration of ~ 1021 cm⁻3. A p-type NiO/n-type AZO heterojunction solar cell on ITO glass, with AZO deposited at 400 °C, achieved 4.5% efficiency, an open-circuit voltage of 844 mV, and a short-circuit current density of 11.3 mA/cm2, highlighting its potential for transparent solar cell applications.