Elaboration of spin coated deposition of tin oxide thin films: Effect of concentration

Tin oxide (SnO₂) thin films were deposited on glass substrates using a cost effective spin coating method. The effect of solution molarity on their microstructural, optical and electrical properties was investigated. For this purpose, solutions of tin chloride salt were prepared with various molarity in the range of 0.1 to 0.25 M. The synthetized films structure and morphology were characterized by different techniques such as: X-rays diffraction (XRD) and scanning electron microscopy (SEM). The optical and electrical properties were studied by mean of UV visible spectroscopy and four probes conductivity measurement. The XRD patterns of all samples revealed well-crystallized and pure SnO₂ films with tetragonal rutile structure. The SEM images reveal a smooth and dense film pinholes free. The optical analyses show that the films exhibit an optical transparency that reaches up to 98 % in the visible range and that the optical band gap decreases from 3.97 to 3.82  eV when the concentration increases from 0.1 to 0.25 M. The films electrical conductivity varies in the range from 76 to 100 (Ω.cm)^-1. The largest figure of merit of 9.8 × 10^-3, was measured in the films prepared at low solution concentration.