Fabrication of bifunctional counter electrode materials for quantum dot sensitized solar cells by using rGO/1T-MoS2 nano composite

Abstract

The metallic molybdenum disulfide (1T-MoS${}_2$) has recently been recognized as a promising counter electrode (CE) material for quantum dot-sensitized solar cells (QDSSCs). However, its poor structural stability has limited its broader application. Herein to address this challenge, diatomic selenium (Se) and nickel (Ni) were doped into MoS${}_2$ to facilitate the phase conversion of 2H-MoS${}_2$ to 1T-MoS${}_2$. This doped material was then integrated with reduced graphene oxide (rGO) via a hydrothermal method to develop a bifunctional Ni-Se-MoS${}_2$/rGO CE material for QDSSCs. The nanocomposite was characterized using XRD, SEM, FTIR, UV–vis spectroscopy, and electrochemical techniques, confirming the successful formation of the rGO/1T-MoS${}_2$ nanostructure. SEM images revealed Ni-Se-MoS${}_2$ loosely packed onto rGO sheets, and the XRD pattern confirmed the presence of the 1T-MoS${}_2$/rGO composite. Electrochemical impedance spectroscopy and cyclic voltammetry demonstrated excellent electrochemical properties, including a low charge transfer resistance (8.52 $\Omega$) and a high electrochemical surface area. Tauc plot analysis showed a reduced bandgap of 1.8 eV for Ni-Se-MoS${}_2$/rGO compared to 2.0 eV for Ni-Se-MoS${}_2$. These improvements significantly enhance electron lifetime, charge transfer, and charge separation, resulting in superior overall performance of QDSSCs. This study highlights Ni-Se-MoS${}_2$/rGO as a highly efficient and stable photovoltaic CE material for QDSSCs.