Controlling 2D/2D Contacts in 2D TMDC Nanostructured Films for Solar-to-Hydrogen Conversion

With the objective to achieve high-performance photoactive 2D films, a variety of large-surface-area, nanostructured films composed of 2D transition metal dichalcogenides (TMDCs) building blocks was successfully self-assembled using a customized, surface-functionalized, metallic sulfide template. Since 2D/2D contacts in these nanostructured films were anticipated to play a crucial role in charge carrier transport properties, control of 2D/2D contact properties was explored by varying 2D building block sizes and film-forming processes. High-resolution transmission electron microscopy (HRTEM) deep characterization of morphological properties of 2D/2D contacts using focused ion beam (FIB) cross-sections reveals a variety of contact configurations mainly depending on the 2D building block thickness. Particularly, the effects of nanostructuration on 2D/2D contact characteristics such as the contact density, plane/plane vs edge/plane contact ratio, and contact boundary angles are clearly demonstrated on a large range of MoS₂, WS₂ and WSe₂ building blocks varying from monolayers to nanoflakes, displaying various thicknesses. Correlations with electrical and photoelectrochemical properties demonstrate that the 2D/2D contact surface area, 2D/2D contact density, and contact boundary angles are key parameters controlling the recombination of photogenerated carriers. These findings are validated both on p-WSe₂ and p-WS₂ nanostructured films with photocurrents up to 4.5 mA cm^-2 for the photoelectrochemical decomposition of H₂O.