Effect of Annealing in Air on the Structural and Optical Properties and Efficiency Improvement of TiO2/CuxO Solar Cells Obtained via Direct-Current Reactive Magnetron Sputtering

In this study, four various titanium dioxide/cuprum oxide (TiO₂/Cu_xO) photovoltaic structures deposited on glass/indium tin oxide (ITO) substrates using the direct-current (DC) reactive magnetron sputtering technique were annealed in air. In our previous work, the deposition parameters for different buffer layer configurations were first optimized to enhance cell fabrication efficiency. In this paper, the effects of post-deposition annealing at 150 °C in air on the optical properties and I-V characteristics of the prepared structures were examined. As a result, significant changes in optical properties and a meaningful improvement in performance in comparison to unannealed cells were observed. Air annealing led to an increase in the reflection coefficient of the TiO₂ layer for three out of four structures. A similar increase in the reflection of the Cu_xO layer occurred after heating for two out of four structures. Transmission of the TiO₂/Cu_xO photovoltaic structures also increased after heating for three out of four samples. For two structures, changes in both transmission and reflection resulted in higher absorption. Moreover, annealing the as-deposited structures resulted in a maximum relative increase in open-circuit voltage (V_oc) by 294% and an increase in short-circuit current (I_sc) by 1200%. The presented article gives some in-depth analysis of these reported changes in character and origin.