Optimizing Al-Doped ZnO Thin Films: Structural, Optical, and Electrical Enhancements for Solar Cells

Abstract

This study reports the synthesis and characterization of Al-doped ZnO (AZO) thin films deposited on glass substrates using the spray pyrolysis technique. The impact of Al doping concentrations (3, 5, and 7%) on the structural, optical, and electrical properties of ZnO thin films was systematically investigated. X-ray diffraction (XRD) analysis confirmed that all films exhibit a polycrystalline wurtzite structure with a preferred (002) orientation, and no secondary phases were detected, indicating the successful incorporation of Al into the ZnO matrix. UV-Vis spectroscopy revealed that Al doping enhances optical transparency, increasing transmittance from 70% (undoped ZnO) to 78% (AlZO-3.00) in the visible range (380–550 nm). The optical bandgap widened from 3.23 to 3.32 eV, attributed to the Burstein–Moss effect. Hall Effect measurements confirmed n-type conductivity, with carrier concentration increasing significantly, leading to improved electrical conductivity, which reached a maximum of 3.37 × 10^–1 Ω^–1 cm^–1 for the AlZO-3.00 film. However, at higher doping levels, carrier mobility saturation limited further conductivity improvements. These findings suggest that Al-doped ZnO thin films are promising low-cost, high-performance alternatives to conventional indium tin oxide (ITO) electrodes for applications in solar cells, optoelectronic devices, and transparent conductive coatings.