Fundamental Efficiency Limits of Transition-Metal Dichalcogenide Solar Cells with Carrier Multiplication and...

Detailed-balance limits for transition-metal dichalcogenide (TMD) solar cells have been reported, but a unified treatment of thickness-dependent optics, carrier multiplication (CM), hot-carrier (HC) extraction, and finite cooling leakage has been lacking. Here, we develop a generalized detailed-balance upper-bound framework that combines energy- and thickness-dependent absorptance, exciton-resolved monolayer absorbance, an experimental CM-yield limit (η_CM ≤ 0.97), and an endoreversible HC engine with a finite cooling coefficient κ. For optically thick absorbers under AM1.5G, the Shockley-Queisser optimum near E_g ≃ 1.3 eV shifts toward ∼1.0 eV, with reversible efficiencies above 50%. CM does not raise the reversible HC limit; at finite κ, it only redistributes part of the same excess photon energy into collected current. Monolayer TMDs show negligible CM benefit, whereas bulk-like TMDs can exhibit large HC gains only when electron-phonon cooling is strongly suppressed. These results identify narrow-bandgap, optically strong TMDs as the more plausible beyond-SQ route.