Excitonic Physics in Emerging 2D Semiconductors: A First-Principles Many-Body Perspective from Photodetection to Solar Energy Conversion.

Chemically and structurally diverse two-dimensional semiconductors exhibit a broad range of excitonic and optical phenomena that have direct implications for optoelectronic functionality. We examine these materials from a first-principles many-body perspective, emphasizing the connection between microscopic excitonic structure and optoelectronic functionality. Reduced symmetry and orbital character produce polarization-selective absorption, while dimensionality, dielectric screening, and exciton fine structure govern binding energies and radiative behavior. In layered systems, interlayer electrostatics and type-II band alignment promote charge separation, whereas exciton-phonon coupling activates indirect optical transitions and shapes temperature-dependent spectra. These mechanisms establish common design principles for excitonic engineering, whereby the dielectric environment, crystal geometry, lattice dynamics, and stacking are used to control exciton properties and tailor optical functionality. This perspective moves beyond description toward the ab initio prediction and design of emerging 2D materials for targeted optoelectronic applications, including polarization-sensitive photodetection and ultrathin solar-energy conversion.