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Abstract Tin sulfide (SnS) bulk ingot material was prepared by direct fusion of the stoichiometric proportions of the constituent elements in vacuum sealed silica tube, following controlled heating and cooling stages. The X-ray powder diffraction pattern indicated that the prepared powder sample belongs to SnS orthorhombic structure. The corresponding lattice parameters are a =0.43196, b=1.11850, and c=0.39746 nm. SnS thin films with different thickness (155, 225, 283, 470 and 585 nm) were prepared by conventional thermal evaporation technique in vacuum pressure of 10-3 Pa, onto glass substrates held at room temperature. The X-ray and electron diffraction study indicates that the asdeposited SnS films of thickness greater than 283 nm are partially crystalline with very small scattering volume. The crystalline nature of the as-deposited thinner SnS films (of thickness ~100 nm) was also confirmed using transmission electron microscope and the corresponding electron diffraction patterns. It was also observed from the X-ray diffraction that when the deposited SnS films being air annealed up to 423 K the observed peaks intensity increases (i.e. increase the crystalinity); however with further increasing in the annealing temperature to 473 K the intensity of the observed peaks begins to decreases. The crystal size increases with increasing the film thickness and also with the increase of the annealing temperature. The EDX analysis of the deposited SnS films reveals that, the as-deposited thinner SnS films as well as thicker films annealed at annealing temperature ≥ 473 K are deviated from stoichiometry. The optical transmission and reflection spectra were recorded for different film thickness in the wavelength range 350-2500 nm, and the data was used to calculate the refractive index, absorption coefficient and optical band gap. It was found that the refractive index of the deposited SnS films increases as the film thickness increase. The dispersion of the refractive index data was described according to the Wemple- DiDomenico single oscillator model whereby, the single-oscillator energy `gap’ (Eo), dispersion energy (Ed), static refractive index (n (0)), static dielectric constant, ε s as well as the other related optical parameters for the investigated SnS film thicknesses were determined. The refractive index data was further analyzed for different film thickness using the known Sellmeier-dispersion relation from which the average oscillator position o λ , average oscillator strength o S , and dispersion parameter ( ) s o E S have been calculated. The analysis of the optical absorption coefficient for the investigated thickness of SnS films reveals the presence of a direct allowed optical transition. The determined optical band gap was found to be decreases with increasing the film thickness. The current-voltage characteristic of SnS indicates ohmic behavior in the measured voltage range 0-9 V. The film resistance measured at room temperature shows considerable decrease with the increase in the film thickness, reach almost constant value for higher film thickness (585 nm which is the best thickness for photovoltaic application). It was also observed that for all of the investigated film thicknesses, the conductivity dependence of temperatures showing normal semiconducting behavior with single linear part within the measured temperature range (300-460 K); indicates one type of conduction mechanisms through thermally activated process. The determined activation energies values were found to be decreased with the increase of the film thickness. The thickness dependence of the film resistivity is analyzed using the effective mean free path model on the basis of classical size effect. The analysis leads to the evaluation of the important physical parameters i.e. effective mean-free-path of the infinitely thick crystalline film and the bulk resistivity. The I-V characteristic of SnS/Ag-CdS/ITO photovoltaic solar cell has been investigated. The obtained result indicates a poorest photovoltaic behavior, which was attributed in the present work to the non homogeneous, granular, loosely adherent, and not pinhole free of the chemically deposited CdS films. These defects beside the mismatch between SnS (orthorhombic structure) and CdS (cubic structure) cause a short circuit and/or large leakage current of the device. |