The potential-dependent trends in Fig. agree with literature spectroelectrochemistry data for thin films of few-layer MoS2 nanosheets and colloidal film electrodes. However, little attention has been paid to the potentialdependent A-exciton lineshape for ML-MoS2 in liquid electrolyte. Fig. shows potential-dependent spectra of the Aexciton peak for another ML-MoS2 sample using identical experimental conditions as Fig. . Two distinct resonances contribute to this convoluted absorption feature. The neutral A-exciton absorbance (A 0 ) dominates at more positive potentials. While at more negative potentials, the negatively charged trion (A -) dominates, resulting in a shoulder feature at 670 nm (see Fig. ). In the section that follows, we describe an approach to quantitatively link the measured absorbance spectrum to carrier concentration using a many-body model of minimal complexity to describe trion formation in ML transition metal dichalcogenides(TMDs) such as MoS2. MND model and fitting procedure to determine 𝒏 Here we adopt a minimal many-body model of a Fermi polaron put forth by Chang and Reichmann. This model, based on the Mahan-Noziéres-De Dominicis (MND) Hamiltonian, computes the effective 𝑛 that best describes the measured absorbance spectrum at each applied potential (E). A key feature of the model is its ability to capture how A 0 and A - resonances shift in energy and transfer oscillator strength between one another as a function of carrier doping concentration. Before we discuss the detailed calculation and fitting procedures, we first describe the predictions of the MND model at positive, intermediate, and negative potentials.