The Influence of Molarity on the Optical and Electrical Properties of Fluorine-Doped Tin Oxide Thin Films Using Spray Pyrolysis Technique

In this study, we focused on optimizing the deposition of fluorine-doped tin oxide (FTO) films on soda lime glass substrates using the spray pyrolysis technique. The sprayed solution was prepared with varying molar concentrations of the precursor solutions (0.3 mol/L, 0.5 mol/L, and 0.7 mol/L) with a fixed molar ratio ([F])/([Sn]) of 0.15 and deposited at fixed temperature of 550 degrees C. The optical and electrical properties of FTO thin films were evaluated based on their optical transmittance and sheet resistance, both combined in a figure of merit (FOM). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses reveal that the films are uniform with a compact and continuous grain distribution, with grain sizes approximately 240 nm, 230 nm, and 200 nm for FTO-1 (M = 0.3 mol/L), FTO-2 (M = 0.5 mol/L), and FTO-3 (M = 0.7 mol/L), respectively. Optical transmission spectra show an inverse relationship with precursor concentration, with FTO-1 achieving the highest transmission of 83.79% at 550 nm. The optical bandgaps were determined using the Tauc method, with values ranging from 3.90 eV to 4.00 eV. An increase in the carrier concentrations (n) and electron mobilities mu of the FTO samples was observed with increasing molarity of the precursors solutions. Measurements carried out using the Hall effect indicate that the carrier concentration is highest for FTO-3 (n = 5.53x10(21)cm(-3)), and the film obtained demonstrates good sheet resistance (R-s = 10 Omega square(-1)). However, FTO-1 exhibits the highest Haacke's figure of merit: empty set = 12.6x10(-3)(Omega square(-1))(-1). The study concludes that the variation in precursor concentration (molarity) significantly impacts the film properties, especially the electrical properties suggesting optimal conditions for specific optoelectronic applications.