Size-Controlled Cu3VSe4 Nanocrystals as Cathode Material in Platinum-Free Dye-Sensitized Solar Cells

In this work, we report the first single-step, size-controlled synthesis of Cu3VSe4 cuboidal nanocrystals, with the longest dimension ranging from 9 to 36 nm, and their use in replacing the platinum counter electrode in dye-sensitized solar cells. Cu3VSe4, a ternary semiconductor from the class of sulvanites, is theoretically predicted to have good hole mobility, making it a promising candidate for charge transport in solar photovoltaic devices. The identity and crystalline purity of the Cu3VSe4 nanocrystals were validated by X-ray powder diffraction (XRD) and Raman spectroscopy. The particle size was determined from the XRD data using the Williamson-Hall equation and was found in agreement with the transmission electron microscopy imaging. Based on the electrochemical activity of the Cu3VSe4 nanocrystals, studied by cyclic voltammetry, the nanomaterials were further employed for fabricating counter electrodes (CEs) in Pt-free dye-sensitized solar cells. The counter electrodes were prepared from Cu3VSe4 nanocrystals as thin films, and the charge transfer kinetics were studied by electrochemical impedance spectroscopy. The work demonstrates that Cu3VSe4 counter electrodes successfully replace platinum in DSSCs. CEs fabricated with the Cu3VSe4 nanocrystals having an average particle size of 31.6 nm outperformed Pt, leading to DSSCs with the highest power conversion efficiency (5.93%) when compared with those fabricated with the Pt CE (5.85%).

Colloidal Synthesis and Photocatalytic Properties of Cu3NbS4 and Cu3NbSe4 Sulvanite Nanocrystals

Niobium sulvanites Cu₃NbX₄ (X = S, Se) have been theoretically predicted as promising candidates for solar photovoltaics and photocatalytic water splitting. This report outlines the first synthesis of Cu₃NbS₄ and Cu₃NbSe₄ in a nanocrystalline form. The crystal structures were investigated by X-ray diffraction, identity was confirmed by Raman spectroscopy, and the optoelectronic properties and morphology of Cu₃NbS₄ and Cu₃NbSe₄ nanocrystals were examined by UV–vis spectroscopy and transmission electron microscopy, respectively. To gain insight into the Cu₃NbX₄ formation, a mechanistic study was conducted for Cu₃NbSe₄ monitoring the nanoparticles’ formation as a function of reaction time. Methylene blue photodegradation tests were conducted to evaluate the photoactivity of Cu₃NbS₄ and Cu₃NbSe₄. The degradation rates, 2.81 × 10^–2 min^–1 and 1.22 × 10^–2 min^–1 proved the photocatalysts’ potential of nanoscale Cu₃NbX₄.

Sulvanites: The Promise at the Nanoscale

The class of ternary copper chalcogenides Cu3MX4 (M = V, Nb, Ta; X = S, Se, Te), also known as the sulvanite family, has attracted attention in the past decade as featuring promising materials for optoelectronic devices, including solar photovoltaics. Experimental and theoretical studies of these semiconductors have provided much insight into their properties, both in bulk and at the nanoscale. The recent realization of sulvanites at the nanoscale opens new avenues for the compounds toward printable electronics. This review is aimed at the consideration of synthesis methods, relevant properties and the recent developments of the most important sulvanites.