The electronic and optical properties of transition metal dichalcogenides are well understood. However, much less are known about the role of defects and free carriers in exciton recombination, which is of fundamental importance for optoelectronic applications. Here, we investigate the photoexcited carrier recombination mechanism in few-layer (4−6 L) MoS 2 nanosheets by employing pump energy and fluence-dependent femtosecond transient absorption spectroscopy. We demonstrate that the multi-particle (excitons and free carriers) generated by 3.1 eV excitation well above the electronic bandgap exhibit distinct recombination times. For instance, free carriers slow down the recombination by orders of magnitude relative to excitons. In contrast, the recombination time of excitons generated upon near quasi-particle excitation (1.94−2.22 eV) drops to ∼3 ps, which is associated with fast exciton capture to defects. To understand the nature of defects, we have investigated different configurations of sulfur vacancies from density functional theory (DFT) and time-dependent DFT.

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We studied many-body dynamics in MoWS2 single-crystal using time and energy-resolved reflection spectroscopy. We detected ultrafast bandgap renormalization, overwhelmed by trap-induced absorption (TIA) at longer timescale. Furthermore, non-decaying TIA caused formation of long-lived trapped exciton.

Photocatalytic processes are among the prime means for mitigating the pollution caused by toxic effluents. In this context, photocatalysis presents a promising path and undergoing rapid evolution. Halide perovskites (HPs) are excellent candidates due to their negative conduction band minimum and the low work function that are essential for photocatalysis. Interestingly, HPs performance significantly improves by introducing transitional-metal dichalcogenides as a co-catalyst, which enables suppressed charge recombination. Here we investigate the photocatalytic performance of Cs4PbBr6/WS2 nanocomposites towards organic dye degradation under visible light illumination. We found that the Cs4PbBr6/WS2 nanostructures significantly increase the degradation rate of methylene blue compared to pristine Cs4PbBr6 nanocrystals. The transient absorption measurements reveal charge transfer from Cs4PbBr6 to WS2. The results of our study imply that the boosted photocatalytic performance of the nanocomposites is due to the reduced carrier recombination. Our findings pave the way for the implementation of Cs4PbBr6/WS2 nanocomposites as superior photocatalysts.

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