Semiconducting transition metal dichalcogenides can be synthesized in a wide range of structures and geometries, including closed cage nanostructures, such as nanotubes or fullerene‐like nanoparticles (NSs). The latter is especially intriguing due to the stability, enhanced light‐matter interactions, and ability to sustain exciton‐polaritons (EPs) in ambient conditions, i. e., strong coupling of excitonic resonances to the optical cavity. Here we investigate the dynamics of EPs formation in WS2 NPs in the time domain using femtosecond transient extinction spectroscopy. We develop a gamut of analytical methods and models with time‐dependent parameters to extract the underlying non‐equilibrium dynamics of EPs formation. We find that the formation of EPs in WS2 NPs is not instantaneous but a gradual process that occurs only after several picoseconds. Specifically, for the short delay times, the light‐matter interaction is guided by excitonic absorption, whereas for the long delay times, the process is controlled by polaritonic scattering. We discover that the coupling strength is a time‐dependent entity and not a constant as is usually defined. Namely, there is a nonlinear coupling between excitonic and external modes and a notable transition from weak to strong coupling limit. Our results show that the time‐dependent phenomenological dynamical model quantitatively reproduces the nonlinear dynamical coupling as well as the effects of the pump fluence on the coupling strength.

We discuss here a solution-processed thin film of antimony trisulphide (Sb 2 S 3 ; band gap ≈ 1.7 eV; electronic configuration: ns 2 np 0 ) for applications in planar heterojunction (PHJ) solar cells. An alternative solution processing method involving a single-metal organic precursor, viz., metal–butyldithiocarbamic acid complex, is used to grow the thin films of Sb 2 S 3 . Because of excess sulphide in the metal complex, the formation of any oxide is nearly retarded. Sb 2 S 3 additionally displays structural anisotropy with a ribbon-like structure along the [001] direction. These ribbon-like structures, if optimally oriented with respect to the electron transport layer (ETL)/glass substrate, can be beneficial for light-harvesting and charge-transport properties. A PHJ solar cell is fabricated comprising Sb 2 S 3 as the light absorber and CdS as an ETL coated on to FTO. With varying film sintering temperature and thickness, the typical ribbon-like structures predominantly with planes hkl : l = 0 stacked horizontally along with respect to CdS/FTO are obtained. The morphology of the films is observed to be a function of the sintering temperature, with higher sintering temperatures yielding compact and smooth films with large-sized grains. Maximum photon to electricity efficiency of 2.38 is obtained for PHJ solar cells comprising 480 nm thick films of Sb 2 S 3 sintered at 350 °C having a grain size of few micrometers (>5 μm). The study convincingly shows that improper grain orientation, which may lead to nonoptimal alignments of the intrinsic structure with regard to the ETL/glass substrate, is not the sole parameter for determining photovoltaics performance. Other solution-processing parameters can still be suitably chosen to generate films with optimum morphology, leading to high photon to electricity efficiency.

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.