Spin coating deposition of tin oxide thin films: Influence of solution concentration

Tin oxide (SnO 2 ) 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 0.1M to 0.25M. The synthesized films structure and morphology were characterized by different techniques such as X-ray diffraction and scanning electron microscopy. The optical and electrical properties were studied by mean of UV-Vis spectroscopy and four probes conductivity measurement. The X-ray diffraction patterns of all samples revealed well-crystallized and pure SnO 2 films with tetragonal rutile structure. The scanning electron microscopy 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 0.1M to 0.25M. 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.