Two-dimensional (2D) transition metal dichalcogenides (TMDCs) such as monolayer MoS₂ exhibit strong excitonic effects and tunable electronic states that make them promising materials for photoelectrochemical energy conversion. In these atomically thin systems, the bandgap is not fixed but undergoes bandgap renormalization (BGR), shifting the conduction (E_CB) and valence (E_VB) band edge positions, in response to changes in carrier concentration and dielectric environment. This research investigates how BGR is induced through screening effects and how BGR influences charge transfer across semiconductor|electrolyte interfaces, thereby modulating electrochemical behavior.

Using in situ spectroelectrochemistry and absorbance spectroscopy coupled with Mahan–Nozières–De Dominicis (MND) computational modeling, excitonic features in monolayer MoS₂ were analyzed as functions of solvent dielectric constant and applied potential. Experimental results reveal that higher dielectric environments enhance exciton formation and suppress trion generation, reducing the bandgap size through a smaller exciton binding energy in accordance with dielectric screening theory. Complementary experimental cyclic voltammetry measurements show that more negative redox potentials and charge-equilibration processes induce bandgap narrowing, increasing overlap between E_CB and acceptor electronic states in solution. Simulated cyclic voltammograms confirm that energy level alignment amplifies current output. Collectively, this work elucidates the interplay between BGR, dielectric screening, and interfacial energetics in 2D semiconductors, providing a mechanistic foundation for designing next-generation photocatalytic and photoelectrochemical materials.