Slow cooling and efficient extraction of C-exciton hot carriers in MoS 2 monolayer

• Published in: Nature communications 2017-01, Vol.8, p.13906
• Main Authors: Wang, Lei, Wang, Zhuo, Wang, Hai-Yu, Grinblat, Gustavo, Huang, Yu-Li, Wang, Dan, Ye, Xiao-Hui, Li, Xian-Bin, Bao, Qiaoliang, Wee, AndrewThye-Shen, Maier, Stefan A, Chen, Qi-Dai, Zhong, Min-Lin, Qiu, Cheng-Wei, Sun, Hong-Bo
• Format: Article
• Language: English
• ISSN: 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 MoS 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 MoS 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.