Efficient Carrier Multiplication Beyond Mo- and W-Based Transition Metal Dichalcogenides: Multilayer HfSe2 and ReSe2

Transition metal dichalcogenides (TMDCs) are layered van der Waals semiconductors that can convert a single high-energy photon into multiple electron–hole pairs through carrier multiplication (CM). However, the factors governing CM efficiency within the TMDC family remain unclear, with studies limited to Mo- and W-based compositions. Here, we address this question by investigating HfSe2 and ReSe2, two less-explored TMDCs with markedly different electronic densities of states. Combining first-principles calculations with ultrafast optical spectroscopy, we establish the occurrence of efficient CM in both materials, with quantum yields 20–30% higher than those of previously studied multilayer TMDCs. Our analysis reveals that CM outcompetes phonon-mediated cooling. Furthermore, we observe similarly high CM efficiencies in HfSe2 and ReSe2 despite their vastly different number of possible CM pathways. This comparison reveals that the CM efficiency is mainly determined by the presence of at least a single CM decay pathway rather than the total number.