Fast Exciton Diffusion in Monolayer PtSe2

Abstract Recently, 2D noble metal dichalcogenides have drawn considerable attention due to their thickness‐tunable electronic and optical properties. However, the dynamical properties of photocarriers in these materials are less studied. Here, photocarrier dynamics in monolayer and bilayer PtSe samples prepared by chemical vapor deposition are studied by transient absorption microscopy. Spatially and temporally resolved differential reflectance measurements yield room‐temperature exciton lifetimes of 25 and 50 ps for monolayer and bilayer samples, respectively. The exciton diffusion coefficient in monolayer PtSe is found to be as large as 48 cm s. This value is higher than exciton diffusion coefficients of most known monolayer semiconductors. The deduced exciton mobility is close to the theoretical limit of charge carrier mobility of monolayer PtSe. The superior exciton transport property is unique to monolayers, as the exciton diffusion coefficient drops to 6.7 cm s in bilayers PtSe. The novel exciton transport properties, along with its high air stability, make monolayer PtSe an attractive material for ultrathin excitonic devices. These results provide insights on the exciton dynamic properties of 2D PtSe and help develop fundamental understanding on the performance of various optoelectronic devices based on 2D PtSe.