Second, we quantify band edge movement by interpolating Eg values as a function of 𝑛. The first problem with this strategy is the accuracy of 𝑛 values obtained using either the MND or WM models. We calculate 𝑛 from the 𝜀 F parameter in the MND model using Eqn. 2, which considers the pristine semiconductor at 0 K. Aside from ignoring the thermally excited carriers, the MND model does not consider the electrolyte, underlying substrate, spin-orbit coupling to treat the B-exciton and Btrion , and defects that could serve as extrinsic dopants in the 2D material. A growing body of evidence has shown that defect concentrations and types, substrate materials, solvent, and surrounding chemical environment 55 all influence 𝑛. Current theory does not consider many practical materials and electrochemical factors. Future theory development is needed to accurately determine 𝑛 using in situ spectroelectrochemistry (e.g., absorbance/reflectance, Raman, or PL spectroscopy). The second problem with the optical spectroscopy strategy proposed herein is it relies also on the accuracy of Eg values as a function of 𝑛. Experimentally measured Eg values show similar BGR trends as the theoretical calculations, but the absolute values can differ by as much as 0.2 eV. The disagreement could be due to the fact the models do not consider defects and substrate/environmental doping effects. Despite the current inaccuracy of calculating 𝑛 and Eg, we believe in situ absorbance measurements, modelled by many-body theory, represent a viable approach to quantify interfacial energetics because there is a robust theoretical framework connecting the observed spectrum to critical parameters relevant to semiconductor energy levels (n and Eg).