Spatial Control of Interlayer Excitons in 2D Metal Tellurohalides for Efficient Excitonic Solar Cells: Probing Excited States under External Perturbations

In atomically thin 2D semiconductors, photoexcitation typically generates excitons with a binding energy of ∼500 meV, which is significantly larger than the thermal energy at room temperature (25 meV). This strong exciton binding limits efficient exciton dissociation, posing challenges for photovoltaic efficiency. Intralayer excitons experience relatively stronger screening than interlayer excitons, resulting in weaker binding for the latter. Despite this, interlayer exciton binding energy in 2D heterostructures remains above 100 meV. This study explores strategies to regulate exciton spatial localization and binding energy, such as dielectric screening and magnetic fields. The research extends beyond the ground state to analyze variations in excited states - 1s, 2s, 3s, 4s, and higher. We demonstrate a reduction in exciton binding energy by an order of magnitude with precise control of μeV. Moreover, the van der Waals heterostructure InTeI/InTeBr exhibits an ultrahigh exciton diffusion length in the micrometer range, along with anisotropy, both of which are beneficial for photovoltaic and optoelectronic applications. This makes it a promising solar cell candidate, achieving an efficiency of 14%.