A study on the Al doping behavior with sol aging time and its effect on structural and optical properties of sol–gel prepared ZnO thin films

• Effects of sol aging-time on the properties of Al-doped ZnO thin films.
• Al atoms doping in to ZnO lattice increased with sol aging up to a certain time.
• Films prepared from 20-24-h aged sol showed minimum surface roughness.
• Optical transmittance of thin films was found sensitive to sol aging time.

A series of aluminum doped zinc oxide (AZO) thin films were prepared by sol–gel method on glass substrates to investigate the behavior of Al doping with sol aging time (as-prepared to 2 weeks). X-ray diffraction analysis revealed a considerable shift in (002) diffraction peak towards higher diffraction angles with increasing sol aging time from as-prepared to 24 h which was found to be reverse with further aging. X-ray photoelectron spectroscopy and UV–vis spectroscopy were performed to investigate the change in chemical states of Al/Zn/O atoms and band gap fluctuations respectively. It was found that more Al atoms were doped into ZnO lattice with the increment of sol aging time and saturated level was achieved for ~ 20–24 h. Field emission scanning electron microscope and atomic force microscope characterization showed dense and homogeneous film morphology with decreasing relative surface roughness with sol aging time. Photoluminescence analysis and UV–vis spectroscopy revealed defect free films by exhibiting high optical transmission in the visible regime and found to improve with sol aging time. It could be concluded that solution aging time clearly influence the doping behavior and a suitable aging provides more stability which results into more Al atoms substitution for Zn in ZnO crystal lattice that affect the structural, morphological and optical properties of AZO thin films.