Ink-jet printing and drop-casting deposition of 2H-phase SnSe$_2$ and WSe$_2$ nanoflake assemblies for thermoelectric applications
The development of simple, scalable, and cost-effective methods to prepare Van der Waals materials for thermoelectric applications is a timely research field, whose potential and possibilities are still largely unexplored. In this work, we present a systematic study of ink-jet printing and drop-casting deposition of 2H-phase SnSe and WSe$_2$ nanoflake assemblies, obtained by liquid phase exfoliation, and their characterization in terms of electronic and thermoelectric properties. The choice of optimal annealing temperature and time is crucial for preserving phase purity and stoichiometry and for removing dry residues of ink solvents at inter-flake boundaries, while maximizing the sintering of nanoflakes. An additional pressing is beneficial to improve nanoflake orientation and packing, thus enhancing electric conductivity. In nanoflake assemblies deposited by drop casting and pressed at 1 GPa, we obtained thermoelectric power factors at room temperature up to $2.2\times 10^{-4}$ mW m$^{-1}$ K$^{-2}$ for SnSe$_2$ and up to $3.0\times 10^{-4}$ mW m$^{-1}$ K$^{-2}$ for WSe$_2$.