Hot carrier diffusion-assisted ideal carrier multiplication in monolayer MoSe2†

Abstract

Carrier multiplication (CM), the process of generating multiple charge carriers from a single photon, offers an opportunity to exceed the Shockley–Queisser limit in photovoltaic applications. Despite extensive research, no material has yet achieved ideal CM efficiency, primarily due to significant energy losses from carrier-lattice scattering. In this study, we demonstrate that monolayer MoSe₂ can attain the theoretical maximum CM efficiency permitted by the energy-momentum conservation principle, using ultrafast transient absorption spectroscopy. By resolving the scatter-free ballistic transport of hot carriers and validating our findings with first-principles calculations, we identify the cornerstone of optimal CM in monolayer MoSe₂: superior hot-carrier dynamics characterized by suppressed energy dissipation via minimized carrier-lattice scattering and the availability of abundant CM pathways facilitated by 2E_g band nesting. Comparative analysis with bulk MoSe₂ further emphasizes the enhanced CM efficiency in the monolayer, attributed by superior hot-carrier diffusion and access to additional CM pathways. These results position monolayer MoSe₂ as a promising candidate for high-performance optoelectronic applications, providing a robust platform for next-generation energy conversion technologies.