Unraveling the Photophysics of Liquid-Phase Exfoliated Two-Dimensional ReS₂ Nanoflakes

Rhenium disulfide (ReS₂) has gained widespread attention in optoelectronic devices such as solar cells, photodetectors, etc., owing to its layer independent optical properties in addition to structural and vibrational anisotropy. For the abovementioned optoelectronic applications, it is crucial to study the generation, mobility, and decay of charge carriers after photoexcitation. In our work, we employed ultrashort laser pulses to photoexcite a thin film of liquid-phase exfoliated ReS₂ and studied the time-resolved generation and response of charge carriers. By terahertz conductivity measurements, we successfully detected the presence of free charge carriers despite the high binding energy of excitons in ReS₂. During the first few picoseconds,  fast decay of free charges due to trapping and/or recombination to excitons was observed. Charges surviving on longer time showed intricate effects on the transient optical spectrum.