Slow cooling and efficient extraction of C-exciton hot carriers in MoS2 monolayer

L. WANG; Z. WANG; H.-Y. WANG; G. GRINBLAT; Y.-L. HUANG; D. WANG; X.-H. YE; X.-B. LI; Q. BAO; A. T. S. WEE; S. A. MAIER; Q.-D. CHEN; M.-L. ZHONG; C.-W. QIU; H.-B. SUN

NATURE COMMUNICATIONS

Nature Publishing Group

Lugar: Londres; Año: 2017 vol. 8 p. 13906 - 13906

2041-1723

In emerging optoelectronic applications, such as water photolysis, exciton fission and novel photovoltaics involving low-dimensional nanomaterials, hot-carrier relaxation and extraction mechanisms play an indispensable and intriguing role in their photo-electron conversion processes. Two-dimensional transition metal dichalcogenides have attracted much attention in above fields recently; however, insight into the relaxation mechanism of hot electron-hole pairs in the band nesting region denoted as C-excitons, remains elusive. Using MoS2 monolayers as a model two-dimensional transition metal dichalcogenide system, here we report a slower hot-carrier cooling for C-excitons, in comparison with band-edge excitons. We deduce that this effect arises from the favourable band alignment and transient excited-state Coulomb environment, rather than solely on quantum confinement in two-dimension systems. We identify the screening-sensitive bandgap renormalization for MoS2 monolayer/graphene heterostructures, and confirm the initial hot-carrier extraction for the C-exciton state with an unprecedented efficiency of 80%, accompanied by a twofold reduction in the exciton binding energy.