Photovoltaic performance in CIGS solar cells: effects of using Mg- and Al-doped ZnO thin-film layers as alternative TCO and front contact layer

In this study, we aimed to improve the electrical, optical, and structural properties of ZnO-based layered CIGS solar cells by doping different ratios of Al and Mg. Al-doped ZnO and Mg-doped ZnO thin films were prepared using sol–gel spin-coating technique. The doping rates were 1%, 3%, and 5% for both materials. Structural, surface, and optical properties were analyzed using XRD, FESEM, AFM, and UV–Vis spectroscopy. The results revealed that Al doping increased surface roughness, while Mg doping decreased it. Al doping reduced the band gap to 3.05 eV, enhancing conductivity, whereas Mg doping increased the band gap to 3.52 eV, improving optical transparency. The ideal combination of AZ5/MZ1 layers achieved a significant efficiency increase of 26.46% in CIGS solar cells, compared to 23.24% with undoped ZnO layers. Additionally, the surface roughness values were found to be 224.3 nm for AZ5 and 69.7 nm for MZ5. This study demonstrates the potential of Al and Mg-co-doped ZnO thin films to improve the performance of solar cells and other optoelectronic devices, offering promising developments in renewable energy technologies.