Coupled Charge Transfer Dynamics and Photoluminescence Quenching in Monolayer MoS₂ Decorated with WS₂ Quantum Dots

Herein, we have investigated the tunability of the photoluminescence (PL) of the monolayer MoS₂ (1L-MoS₂) by decorating it with WS₂ quantum dots (WS₂ QD). The direct bandgap 1L-MoS₂ and WS₂ QDs are grown by chemical vapor deposition and liquid exfoliation methods, respectively. The room temperature PL spectrum of bare 1L-MoS₂ is systematically quenched with its decoration with WS₂ QDs at different concentrations. A decrease in the work function of 1L-MoS₂ with the decoration of WS₂ QDs was established from the Kelvin probe force microscopy analysis. A detailed quantitative analysis using the four-energy level model involving coupled charge transfer was employed to explain the redshift and the systematic decrease in the intensity of the PL peak in 1L-MoS₂/WS₂ QD heterostructure. The modulation of the PL in the heterostructure is attributed to the increase in the formation of negative trions through the charge transfer from WS₂ QD to the 1L-MoS₂ and thus making the 1L-MoS₂ heavily n-type doped, with increase in the electron density by ~1.5 × 10¹³ cm^-2. This study establishes the contribution of defects in the coupled charge transfer dynamics in 1L-MoS₂, and it lays out a convenient strategy to manipulate the optical and electrical properties of 1L-MoS₂ for various optoelectronic applications.