Auger-Assisted Secondary Hot Carrier Transfer in a Type I MoS2/PtSe2 Heterostructure

Charge transfer is vital in determining the optoelectronic properties of atomically thin materials, yet remains elusive in type I heterostructures. Here, distinct two-step charge transfer processes in a type I MoS2/PtSe2 heterostructure are reported. By exclusively exciting the smaller bandgap PtSe2, strong exciton photobleaching peaks of the larger bandgap MoS2 are observed, indicating primary hot carrier transfer from PtSe2 to MoS2 within 70 fs. More importantly, the amplitude of the exciton peaks shows a secondary increase after the initial rapid decay. These dynamics are distinctly different from the monotonic decrease in monolayer MoS2 and indicate a secondary charge transfer process that is attributed to hot carriers re-generated in PtSe2 by intralayer Auger recombination. Concurrently, the exciton energy blue shifts within 100 ps, probing the dynamic buildup of a charge-transfer induced electric field across the heterostructure interface, which displaces electron and hole wavefunctions of MoS2 excitons and reduces the exciton binding energy. The results are corroborated by carrier dynamics and transient absorption spectra simulations by considering the two-step charge transfer processes. The work reveals Auger-assisted hot carrier transfer processes in type I heterostructures and suggests the possibility for optoelectronic and photocatalytic applications by optical sub-bandgap excitation.