The role of excitons and free charges in the excited-state dynamics of solution-processed few-layer MoS₂ nanoflakes

Tsokkou, Demetra; Yu, Xiaoyun; Sivula, Kevin; Banerji, Natalie

doi:10.1021/acs.jpcc.6b09267

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The role of excitons and free charges in the excited-state dynamics of solution-processed few-layer MoS₂ nanoflakes

Tsokkou, Demetra Department of Chemistry, University of Fribourg, Switzerland
Yu, Xiaoyun Laboratory for Molecular Engineering of Optoelectronic Nanomaterials, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland
Sivula, Kevin Laboratory for Molecular Engineering of Optoelectronic Nanomaterials, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland
Banerji, Natalie Department of Chemistry, University of Fribourg, Switzerland

13.10.2016

Published in:

The Journal of Physical Chemistry C. - 2016, vol. 120, no. 40, p. 23286–23292

English Solution-processed semiconducting transition metal dichalcogenides are emerging as promising two-dimensional materials for photovoltaic and optoelectronic applications. Here, we have used transient absorption spectroscopy to provide unambiguous evidence and distinct signatures of photogenerated excitons and charges in solution- processed few-layer MoS₂ nanoflakes (10–20 layers). We find that photoexcitation above the direct energy gap results in the ultrafast generation of a mixture of free charges in direct band states and of excitons. While the excitons are rapidly trapped, the free charges are long-lived with nanosecond recombination times. The different signatures observed for these species enable the experimental extraction of the exciton binding energy, which we find to be ∼80 meV in the nanoflakes, in agreement with reported values in the bulk material. Carrier-density-dependent measurements bring new insights about the many-body interactions between free charges resulting in band gap renormalization effects in the few-layer MoS₂ nanoflakes.

Faculty

Faculté des sciences et de médecine

Department

Département de Chimie

Language