Near Unity Molecular Doping Efficiency in Monolayer MoS2

TL;DR

This study measures and demonstrates high doping efficiency of organic electron donors on monolayer MoS2, achieving the highest doping levels reported and aligning with theoretical predictions, thus guiding future design of dopants.

Contribution

It provides the first quantitative measurement of doping efficiency for organic electron donors on MoS2 and identifies a stronger dopant than previously used ones.

Findings

Doping efficiency ranges from 0.63 to 1.26 electrons per molecule.

Achieved the highest doping level in monolayer MoS2 via surface functionalization.

Doping efficiencies align with first-principles calculations.

Abstract

Surface functionalization with organic electron donors (OEDs) is an effective doping strategy for two-dimensional (2D) materials, which can achieve doping levels beyond those possible with conventional electric field gating. While the effectiveness of surface functionalization has been demonstrated in many 2D systems, the doping efficiencies of OEDs have largely been unmeasured, which is in stark contrast to their precision syntheses and tailored redox potentials. Here, using monolayer MoS2 as a model system and an organic reductant based on 4,4-bipyridine (DMAP-OED) as a strong organic dopant, we establish that the doping efficiency of DMAP-OED to MoS2 is in the range of 0.63 to 1.26 electrons per molecule. We also achieve the highest doping level to date in monolayer MoS2 by surface functionalization and demonstrate that DMAP-OED is a stronger dopant than benzyl viologen, which was the previous best OED dopant. The measured range of the doping efficiency is in good agreement with the values predicted from first-principles calculations. Our work provides a basis for the rational design of OEDs for high-level doping of 2D materials.