The Role of Excitons and Free Charges in the Excited-State Dynamics of Solution-Processed Few-Layer MoS2 Nanoflakes

• Published in: Journal of physical chemistry. C 2016-10, Vol.120 (40), p.23286-23292
• Main Authors: Tsokkou, Demetra, Yu, Xiaoyun, Sivula, Kevin, Banerji, Natalie
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.6b09267

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.