Fabrication of aluminium modified Bi2O3 thin film as a transparent conductive oxide for optoelectronic applications

Bismuth oxide (Bi2O3) is considered the best oxygen ion conductor due to its crystal structure (fluorite type) and a high percentage of oxygen vacancies up to 25%. The possibility of obtaining Bi2O3 at low temperatures is of great interest. In this study, the first aluminium-modified bismuth oxide (Al-Bi2O3) thin films as a potential transparent conductive oxide (TCO) were electrochemically deposited in a potential window of -1.5 V and + 1.8 V at room temperature onto a fluorine doped tin oxide (FTO) substrate. The electrodeposition of Al-Bi2O3 film was confirmed by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), profilometry and Fourier transform infrared (FTIR) spectroscopy. The electrodeposition of Al-Bi2O3 films followed by heat treatment at 400 °C for 30 min showed the successful formation defect-free transparent films in a relatively simple methodology. The XRD analysis revealed the poly-crystalline nature of the cubic phase of Bi2O3 along with the tetragonal phase of Al2O3 confirming the successful formation of Al-Bi2O3 films. While cyclic voltammetry (CV) was used to study the electrochemical behaviour and charge transfer kinetics during the formation of Al-Bi2O3 films, the ultraviolet-visible (UV-Vis) spectroscopy was used to analyse optical properties and direct band gap of formed Al-Bi2O3 films. The resistivity measurements showed bulk resistivity value of 1.04 × 10− 4 Ω cm suggesting mixed ionic–electronic conduction behaviour. Although Bi₂O₃ is known for high oxygen-ion conductivity at elevated temperatures, the measured room-temperature resistivity and linear I–V characteristics indicate that electronic conduction dominates under the present measurement conditions. Thus, this study demonstrates a simple methodology to fabricate Al-Bi2O3 thin films for next-generation TCOs, warranting further exploration and potential integration into advanced electronic and energy applications.