Effect of Cd doping on the structural, optical, and photovoltaic properties of SnS films

Abstract

This paper reports the fabrication of (0 wt. %, 0.5 wt. %, 1 wt. %, 1.5 wt. %, and 2 wt. %) cadmium-doped tin sulphide (Cd-SnS) thin films using sol-gel technique via green synthesis route. Aloe vera gel is used as a green extract to fast fabricate Cd-SnS films. X-ray diffraction (XRD), UV-Vis spectrophotometer, four-point probe method, and J-V measurements are used to determine the crystallographic structure, optical, electrical, and photovoltaic properties, respectively. Here, the detailed structure properties like crystallite size, dislocation line density, d-spacing, and lattice constants of pure and Cd-SnS films are calculated. XRD confirmed the Cd doping in SnS with an orthorhombic structure. The film of 1.5% Cd-SnS showed good structural properties like large crystallite size (29 nm), small d-spacing (2.82 Å), small dislocation line density (1.18 × 1015 m−2), and lattice constants (a = 11.86 Å, b = 3.92 Å, c = 4.33 Å). Optical parameters like bandgap energy (Eg), extinction coefficient (k), refractive index (n), and dielectric constants (n) are calculated by using a UV-Vis spectrophotometer. Cd doped decreased the Eg of SnS. The low value of Eg (1.40 eV) is observed by 1.5% of Cd doping in SnS. A four-point probe approach is used to evaluate the sheet resistivity of Cd-SnS thin films at ambient temperature. The reduced value of sheet resistivity (1.3 × 104 Ω-cm) is achieved at 1.5% Cd doping. Solar cells of these films are fabricated. The geometry of the Cd-SnS solar cell is glass/FTO/TiO2/SnS/P3HT/Au. The open-circuit voltage (Voc), fill factor (FF), efficiency (η), and short circuit current density (Jsc) of solar cells are determined using a J-V curve. For pure SnS based solar cells, Voc is 0.702 V, Jsc is 2.04 mA cm−2, FF is 0.578, and η is 0.82%. All the factors except Voc are increased by Cd doping. The highest efficiency (1.34%) is obtained using a 1.5% Cd-doped SnS film-based solar cell. This efficiency is 61% higher than pure SnS based solar cells. These cells have a low-cost and long life time because there is no chemical corrosion like dye-sensitized solar cells.