Synthesis and investigation of structural and high temperature conduction mechanism of TiO₂/N-GQDs nanocomposite thin films as a transparent conducting material

This study includes the synthesis and characterization of N-GQDs, pure TiO₂, and TiO₂/N-GQDs nanocomposites thin films prepared by spin-coating technique. The gel of TiO₂ nanoparticles and N-GQDs was prepared using sol–gel and hydrothermal techniques, respectively. Further, the TiO₂/N-GQDs nanocomposites were prepared by sol–gel method in the weight % ratio of 90 TiO₂/10 N-GQDs and 80 TiO₂/20 N-GQDs. The structural, optical and electrical behaviour of these thin film has been investigated using XRD, AFM, HR-TEM, UV–Visible spectroscopy and two probe methods. The XRD study had confirmed the tetragonal structure of TiO₂. The average crystallite size calculated using Debye–Scherrer’s equation has been found to be 13.56 nm for TiO₂ which decreases up to 11.31 nm for 80 TiO₂/20 N-GQDs. The HR-TEM analysis had confirmed the successful formation of N-GQDs having the average particle size about 8.63 nm. Further, the optical band gap was found to be 4.07 eV, 3.28 eV for N-GQDs, TiO₂ which increases up to 3.69 eV for 80 TiO₂/20 N-GQDs thin film. Also, it has been observed that the prepared thin films are highly transparent in visible region. Further, the temperature dependent I–V characteristics of prepared thin films within the temperature range of 293–513 K and voltage range of 0–60 V depicts the decreased resistivity up to 1.85 × 10⁴ Ω–cm at 513 K from 3.35 × 10⁴ Ω–cm at 293 K of 80 TiO₂/20 N-GQDs thin film. Moreover, the increase in the transparency of 80 TiO₂/20N-GQDs thin film and decreased resistivity up to 1.85 × 10⁴ Ω–cm at 513 K suggests its utilization as a transparent and conducting electrode in optoelectronic devices.