Few-layer 2D transition metal dichalcogenides with high catalytic performance as efficient counter-electrodes in solar cells

Spyros Yannopoulos, ICE/HT, FORTH, Rio-Patras, GREECE
George Syrrokostas, Ice/ht, Forth, Rio-patras, Greece
Aspasia Antonelou, Ice/ht, Forth, Rio-patras, Greece
Vasileios Dracopoulos, Ice/ht, Forth, Rio-patras, Greece

Two-dimensional (2D) crystals have attracted a tremendous amount of research interest over the last decade owing to their unique properties in comparison to their bulk counterparts. The interest is not only academic as 2D crystals exhibit a number of unique phenomena exploitable in various applications. Besides single-atom thick 2D crystals such as graphene, polyhedral thick materials whose layer thickness is dictated by the size of structural unit, i.e. transition metal di-chalcogenides, TMDCs (MoX2, TaX2, etc., with X: S, Se, Te) can be prepared in mono- and few-layer thickness by various methods.
Whilst the vast majority of the spectacular properties of TMDCs emerging as the number of monolayers decreases are so far considered adequately understood, vivid interest is focused now on commercialization and viable applications of these materials. Essentially, the prerequisite to achieve this is the facile, reliable and low-cost preparation of substrate-wide films of controlled thickness. Here, we show that preparation of substrate-wide MoX2 is achievable with easy control down to the monolayer thickness. The growth takes place via soft chalcogenation of commercially available Mo foils without any pretreatment by a process that is scalable to any substrate dimension. The quality of the prepared MoX2 layers on such flexible substrates is characterized by Field-Emission Scanning Electron Microscopy (FE-SEM), Raman scattering and X-ray photoelectron spectroscopy (XPS). In addition, the catalytic activity and stability of MoX2 as counter electrodes (CE) has been evaluated demonstrating outstanding performance, better to that of the more costly Pt-based CEs.