Efficient Light Absorption Using ZnS doped on metal for quantum dot-sensitized solar cell

In this work, the CdS/CdSe multi-layers were coated on the ZnS:Cu²⁺ passivation layer to reduce the dark current density and enhance the photon absorption intensity. The passivation layer was fabricated using the SILAR method with different Cu/Zn atom ratios of 0%, 0.1%, 0.3%, 0.5%, 0.7%, and 1.0%, respectively. The photoanode was structurally characterized by XRD and FESEM equipment. It was also studied for optical properties by UV–Vis spectroscopy and electrochemical properties by J-V curves, and electrochemical impedance spectra. As a result, there is a shift peak in the absorption spectrum in the visible light region of films when Cu²⁺ ions were doped on the pure ZnS film. Furthermore, this result was also demonstrated when quantum dot-sensitized solar cells were recorded using the J-V curves. The performance of all cells containing ZnS:Cu²⁺ has a higher current density (J_SC ~ 18.11 mA cm⁻²–22.05 mA cm⁻²) than the photoanode with pure ZnS (J_SC ~ 16.85 mA cm⁻²). The results show an increase in the conversion efficiency of the cell because of reducing excited electrons from CdS/CdSe quantum dots to the polysulfide electrolyte, the appearance of Cu²⁺ energy levels in the band gap of ZnS causes an increase in photon absorption. In addition, the values of dynamic resistance R_ct1 and R_ct2 were determined from the electrochemical impedance spectrum are the smallest (11.88 Ω, and 115.56 Ω) at a doping concentration of 0.5%. It shows that excited electrons move easily and reduce recombination processes in the photoanode.