Enhancement of Structural, Optical and Electrical Properties of Absorber Cu_xS Thin Films and Fabrication of CdS/Cu_xS Heterojunctions Photovoltaic Cells

Copper sulfide (Cu_xS) thin films were elaborated using chemical bath deposition technique (CBD) in order to study their possible use as absorber thin films in cadmium sulfide (CdS)/copper sulfide (Cu_xS) heterojunctions photovoltaic cells. The bath was formed with a mixture of copper chloride (CuCl₂ ⋅ 2H₂O) and thiourea (CS(NH₂)₂) aqueous solutions. Cu_xS thin films were prepared at different deposition times, onto glass substrates at 37°C. The influence of deposition time on the growth kinetics as well as the structural, morphological, atomic composition, optical and electrical properties of the samples was investigated. These physical properties of the thin films were improved by the increase in the deposition time; thus the value of x of Cu_xS increased with the increase of the deposition time. Thickness enlarged, crystalline structure improved, transmittance decreased, band gap increased, Urbach energy reduced and electrical conductivity enhanced with increase of deposition time and x value. In electrical characterization the Ohmic responses were shown in all Cu_xS thin films by the current–voltage (I–U) plots; the electrical conductivity values were subsequently deduced. The as-deposited, illuminated and thermal annealed CdS/Cu_xS heterojunctions were manufactured; knowing that their I–U characteristics exhibited having a well cleared rectifying behavior. The forward voltages (V_F) of the as-deposited, illuminated and annealed structures were deduced. Furthermore, from I–U characteristics the diodes parameters: series resistances (R_s), reverse saturation current (I₀) and ideality factor (n) were deduced and the I–U corrected characteristics were showed. Illumination and thermal annealing were found to considerably enhance the performance of the CdS/Cu_xS photovoltaic cells.