Using Intercalation Chemistry to Change Interlayer Spacing and Resulting Bandgap of Two-Dimension Materials

The operating principle behind smart windows is that they can transmit, absorb or reflect different wavelengths of light at will. To achieve these properties, they must be constructed with materials that have an easily tunable bandgap, this is often done via intercalation chemistry. 2D materials have shown similar tunablity in the past and often show enhanced mobility for ions. We are exploring one such material, WO₂Cl₂, and what role interlayer spacing plays in the bandgap of 2D materials. When WO₂Cl₂ is intercalated with Li, it starts as a wide bandgap material (clear) then transitions to a blue narrower bandgap material, then a coppery metallic phase. To understand these phases, we have carried out 4-point resistivity measurements, absorption and Raman spectroscopy, XRD, XPS, SEM, and TEM. These methods have shown intercalated WO₂Cl₂ to be a very tunable and versatile material. Additionally, we hypothesize a direct relationship between bandgap, interlayer spacing and ion size for WO₂Cl₂. To test this, we have examined properties of WO₂Cl₂ that has been intercalated ions of increasing size, Li<Na<K<Rb<Cs to great success.