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F and Nb + F co-doped SnO2 thin films were deposited on glass substrates by the spray pyrolysis method. The microstructural, morphological, electrical and optical properties of the 10 wt% F doped SnO2 (FTO) thin films were investigated specifically for niobium (Nb) doping in the range of 0–4 at.% with 1 at.% steps. As shown by the x-ray diffraction patterns, the films exhibited a tetragonal cassiterite structure with (200) preferential orientation. It was observed that grain sizes of the films for (200) and (301) peaks depended on the Nb doping concentration and varied in the range of 25.11–32.19 and 100.6–183.7 nm, respectively. The scanning electron microscope (SEM) micrographs showed that the FTO films were made of small pyramidal grains, while doubly doped films were made of small pyramidal grains and big polyhedron grains. From electrical studies, although 1 at.% Nb doped FTO films have the lowest sheet resistance and resistivity values, the highest figure-of-merit and optical band gap values obtained for FTO films were 16.2 × 10−2 Ω−1 and 4.21 eV, respectively. Also, infrared reflectivity values of the films were in the range of 97.39–98.98%. These results strongly suggest that these films are an attractive candidate for various optoelectronic applications and for photothermal conversion of solar energy.

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Bismuth (Bi) doped zinc oxide (ZnO:Bi) thin lms were prepared on glass substrates by solgel spin coating technique using homogeneous precursor solutions, and eects of Bi doping on the structural and optical properties of ZnO were investigated. The crystalline of ZnO lms shifted from polycrystalline nature to amorphous nature with Bi doping. The plane stresses (σ) for hexagonal ZnO and ZnO:Bi crystals were calculated according to the biaxial strain model. The Urbach rule was studied as a function of non-thermal component to the disorder (defects in crystal structures) which is especially observed in the case of non-crystal semiconductors. The calculated Urbach energies and steepness parameters of undoped ZnO and ZnO:Bi lms varied between 44.33 meV and 442.67 meV, and 58.3 × 10 −2 and 5.8 × 10 −2 , respectively. The Urbach energies of the lms increased with an increase in the Bi doping concentration and a great dierence was observed for 7.0 mol.% doping. The band gap values of the lms exhibited a uctuated behavior as a result of doping eect.

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