Tungsten diselenide

Tungsten diselenide

Identifiers
CAS Number	12067-46-8
EC Number	235-078-7
Jmol 3D model	Interactive image
PubChem	82910
InChI InChI=1S/2Se.W Key: ROUIDRHELGULJS-UHFFFAOYSA-N
SMILES [Se]=[W]=[Se]
Properties
Chemical formula	Se2W
Molar mass	341.76 g/mol
Appearance	grey to black solid
Odor	odorless
Density	9.32 g/cm3
Melting point	> 1200 °C
Solubility in water	insoluble
Structure
Crystal structure	hP6, space group P6 3/mmc, No 194
Lattice constant	a = 0.3297 nm, c = 1.2982 nm
Coordination geometry	Trigonal prismatic (WIV) Pyramidal (Se2−)
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Tungsten diselenide is an inorganic compound with the formula WSe₂. The compound adopts a hexagonal crystalline structure similar to molybdenum disulfide. Every tungsten atom is covalently bonded to six selenium ligands in a trigonal prismatic coordination sphere while each selenium is bonded to three tungsten atoms in a pyramidal geometry. The tungsten–selenium bond has a length of 0.2526 nm, and the distance between selenium atoms is 0.334 nm. Layers stack together via van der Waals interactions. WSe₂ is a very stable semiconductor in the group-VI transition metal dichalcogenides.

Synthesis

Heating thin films of tungsten under pressure from gaseous selenium and high temperatures (>800 K) using the sputter deposition technique leads to the films crystallizing in hexagonal structures with the correct stoichiometric ratio.

W + 2 Se → WSe₂

Potential applications

Atomic image of a WSe₂ monolayer showing hexagonal symmetry and three-fold defects. Scale bar: 2 nm (0.5 nm in the inset).

Transition metal dichalcogenides are semiconductors with potential applications in solar cells. WSe
₂ has a band-gap of ~1.35 eV with a temperature dependence of -4.6×10⁻⁴ eV/K. WSe
₂ photoelectrodes are stable in both acidic and basic conditions, making them potentially useful in electrochemical solar cells.

The properties of WSe
₂ monolayers differ from those of the bulk state, as is typical for semiconductors. Mechanically exfoliated monolayers of WSe
₂ are transparent photovoltaic materials with LED properties. The resulting solar cells pass 95 percent of the incident light, with one tenth of the remaining five percent converted into electrical power. The material can be changed from p-type to n-type by changing the voltage of an adjacent metal electrode from positive to negative, allowing devices made from it to have tunable bandgaps. As a result, it may enable LEDs of any color to be made from a single material.