Sol-gel deposition of TiO2 thin films by spin coating for photovoltaic applications: Effect of acetylacetone stabilizer on structural and optical properties

Titanium dioxide (TiO2) is a transparent, conductive photocatalyst widely used in photovoltaic cells (perovskites, DSCC, etc.) [1], [2], [3]. Its low electron-hole separation coefficient due to its limited UV photo-catalytic activity (5%) prevents its optimal use in photovoltaic cells [2]. In this work, we develop TiO2 thin films using the sol–gel method combined with the spin-coating deposition technique, and investigate the structural and optical properties of these thin films for photovoltaic applications. The optimal number of spin cycles leading to improved structural and optical properties of TiO2 layers on a glass substrate is first determined, and the effect of the acetylacetone stabilizer on the structural and optical properties of this sample at optimal number of spin cycles is then investigated.Two differents sol–gel solutions (S and SACact) were used, each composed of: titanium (IV) isopropoxide precursor 98 % concentration 0.36 M, ethanol, acetic acid, distilled water and acetylacetone stabilizer (only for the SACact solution). These sol–gel solutions were deposited on glass substrates and spun at 3000 rpm for 30 s at different centrifugation cycles. Pre-annealing and annealing of the thin films were carried out at 100 °C for 10 min and at 400 °C for 1 h 25 min respectively. The results of the X-ray diffraction (XRD) and UV–Vis analyses reveal more optimal structural and optical properties for the TiO2 thin film at three cycles of spin elaborated with a sol–gel solution treated with acetylacetone stabilizer. For this thin film, XRD show an intense preferential orientation in the (101) direction with microstructural parameters corresponding to the tetragonal anatase structure. UV–Vis analysis shows a strong UV absorption at wavelength 317 nm with an average transmittance reaching 80 % in the visible range and an indirect gap energy of 3.11 eV, justifying a shift of the absorption spectrum into the visible range. These experimental results, compared with other reported work, confirm the optimal use of our 3 spin TiO2 thin films treated with the acetylacetone stabilizer for photovoltaic applications.