Thermal energy mediated enhancement in microstructural and optoelectronic properties of Al-doped MZO thin film

Magnesium-doped Zinc Oxide (MZO) stands out as a potentially effective buffer layer for CdTe solar cells, mainly because of its high transparency, good electrical conductivity, durability in elevated temperatures, and cost-effectiveness. This research involved the co-doping of aluminum-doped zinc oxide (AZO) with magnesium-doped zinc oxide (MZO) through the utilization of both DC and RF co-sputtering techniques. The resulting Al–Mg co-doped ZnO (AMZO) thin films were deposited at various substrate temperatures, ranging from room temperature (∼25 °C) to 300 °C. The structural analysis indicated that the substrate temperature of 25 °C yielded the largest crystallite size. The UV–Vis spectroscopy results showed that all the films possessed transmittance values around 97 %, and the optical bandgap (Eg) ranged from approximately 3.35 to 3.43 eV, elucidating that the optical properties were not significantly influenced by the substrate temperature. Hall effect measurement results indicated that the carrier concentration of the films was in the range of 10¹⁷ - 10¹⁹ cm⁻³, along with a resistivity range of 6.2–16.6 Ω-cm. Due to the trivial impact of substrate temperatures on the structural and optoelectronic properties, post-deposition annealing was conducted at an optimized temperature of 550 °C. As a consequence, the optical bandgap expanded from approximately 3.35 eV for the as deposited film to roughly 3.52 eV for the annealed film. The carrier concentration also rose from nearly 10¹⁹ cm⁻³ to approximately 10²⁰ cm⁻³. Meanwhile, there was a notable decline in resistivity from around 10¹ to ∼10⁻³ Ω-cm, reflecting a noticeable improvement in electrical properties. This investigation illustrates a promising avenue for optimizing the MZO buffer layer, potentially enhancing the efficiency of CdTe solar cells.