Synthesis and characterization of Ag-doped CdS quantum dots for enhanced photovoltaic performance of quantum dot sensitized solar cells

Abstract

In this work, Ag-doped and undoped CdS quantum dots (QDs) were prepared via successive ionic layer adsorption and reaction (SILAR) technique, followed by their characterization. The synthesized QDs were employed in the devices based on iodide/triiodide (I−/I3−) and polysulfide (Sx2−/S2−) electrolytes, while carbon (C) and platinum (Pt) were used as counter electrodes (CEs). The structural properties of the synthesized QDs were examined using X-ray diffraction (XRD), while to analyze the elemental composition of the samples, energy-dispersive X-ray (EDX) spectroscopy technique was employed. To study absorption properties, UV–Visible spectroscopy was performed. The influence of Ag on passivation of defects in CdS QDs was investigated via photoluminescence spectroscopy. Photovoltaic performance and impedance spectroscopic measurements on the fabricated QDSSCs were made under an AM1.5G illumination and dark, respectively. The photovoltaic studies on the devices revealed an increase of efficiency by 131 %, 161 %, 151 %, and 93 % for Ag–CdS QDs/Iodolyte/Pt, Ag–CdS QDs/Polysulfide/Pt, Ag–CdS QDs/Iodolyte/C, Ag–CdS QDs/Polysulfide/C type devices, respectively. The doped device with a polysulfide electrolyte and C as counter electrode (CE) revealed superior performance, exhibiting an efficiency of 1.72 %, followed by the doped polysulfide-based device with Pt as CE, revealing 1.67 % efficiency. The stability test conducted on the fabricated devices demonstrated a long-term stability for the doped device containing polysulfide electrolyte and C as CE, retaining 80 % of its initial efficiency for 12 days, and then falling to 0 % in 22 days. Moreover, the impedance spectroscopic measurements revealed lowest series resistance (Rs) and Series Capacitance (Cs) for the superior performance device.