Fluorine-doped SnO₂ thin films for solar cells: Development and comparative analysis of spray pyrolysis and spin coating techniques

Abstract In this study, fluorine-doped tin oxide (FTO) thin films were synthesized using two low-cost solution-based techniques, homemade spray pyrolysis and spin coating, conducted at a substrate temperature of 500 °C. Fluorine was introduced as an n-type dopant in concentrations ranging from 10 to 40 wt% to enhance the electrical conductivity and optical transmittance of the films. The structural, morphological, and optoelectronic properties of the films were characterized via XRD, SEM, UV-Vis spectroscopy, and Hall effect analysis. The spray-deposited FTO films exhibited superior performance, with optimized samples (at 30 wt% F) achieving a sheet resistance of 20 Ω/□, optical transmittance of 80%, and a figure of merit (FOM) of 5.37×10⁻³ Ω⁻¹. In contrast, spin-coated films showed higher resistivity, lower mobility, and reduced FOM (e.g., 1.53×10⁻³ Ω⁻¹ at 840 nm thickness), attributed to inferior film densification and increased structural defects. The results demonstrate that spray pyrolysis enables the formation of dense, well-crystallized FTO layers with enhanced carrier transport and transparency, making it a more suitable deposition technique for optoelectronic and photovoltaic applications.