The surface and structural characterization techniques of three atom-thick bi-dimensional 2D-WS₂ colloidal nanocrystals cross the limit of bulk investigation, offering the possibility of simultaneous phase identification, structural-to-morphological evaluation, and surface chemical description. In the present study, we report a rational understanding based on X-ray photoelectron spectroscopy (XPS) and structural inspection of two kinds of dimensionally controllable 2D-WS₂ colloidal nanoflakes (NFLs) generated with a surfactant assisted non-hydrolytic route. The qualitative and quantitative determination of 1T’ and 2H phases based on W 4f XPS signal components, together with the presence of two kinds of sulfur ions, S₂²⁻ and S²⁻, based on S 2p signal and related to the formation of WS₂ and WO_xS_y in a mixed oxygen-sulfur environment, are carefully reported and discussed for both nanocrystals breeds. The XPS results are used as an input for detailed X-ray Diffraction (XRD) analysis allowing for a clear discrimination of NFLs crystal habit, and an estimation of the exact number of atomic monolayers composing the 2D-WS₂ nanocrystalline samples.

With the main objective being to develop photochromic smart textiles, in this paper, we studied the photochromic behavior of WO_3-x nanocrystals (NCs) cooperatively interacting with variable amounts of TiO₂ NCs. We tested several blends of WO_3-x:TiO₂ NCs, admixed in different compositions (relative molar ratio of 4:0, 3:1, 2:2, 1:3, 0:4) and electrostatically interfacing because of opposite values of Z-potential, for photo-induced chromogenic textiles. We further monitored the photochromic sensitivity of NC-impregnated textiles after exposure to a few solvents (i.e., methanol, ethanol, and isopropanol) or when over-coated with different polymeric matrices such as natural cellulose or ionic conductive Nafion. The optimization of the compositions of the WO_3-x:TiO₂ blends embedded in polymeric matrices, allowed the nanostructured photochromic textiles to show rapid and tunable coloration (<5 min) and bleaching kinetics (~5 in at 75 °C or 6 h at room temperature) along with good recovery and cycling stability. This study features a simple strategy for the widespread application of WO_3-x:TiO₂-based photochromic smart textiles.

Thanks to their high stability, good optoelectronic and extraordinary electrochromic properties, tungsten oxides are among the most valuable yet underexploited materials for energy conversion applications. Herein, colloidal one-dimensional carved nanocrystals of reduced tungsten trioxide (WO_3−x) are successfully integrated, for the first time, as a hole-transporting layer (HTL) into CH₃NH₃PbI₃ perovskite solar cells with a planar inverted device architecture. Importantly, the use of such preformed nanocrystals guarantees the facile solution-cast-only deposition of a homogeneous WO_3−x thin film at room temperature, allowing achievement of the highest power conversion efficiency ever reported for perovskite solar cells incorporating raw and un-doped tungsten oxide based HTL.

Non-hydrolytic synthesis assisted by long-chain amphiphilic surfactant is exploited to generate dimension-controllable 2D-WS₂ nanoflakes in a single-step protocol, where the chemical nature and steric hindrance of the alkylamine are the key points to modulate the lateral size finally achieved.