An optoelectronic material with a spatially varying bandgap can be applied to a wide range of energy and sensing applications such as photovoltaics, photocatalysis, photodetection, bandpass filters for high-frequency applications, and light-emitting devices.
The efficiency of many optoelectronic devices is limited by spectrum loss (i.e. only photons within a specific energy range are useful). By twisting a van der Waals' Bilayer, this technology creates tunable spatially dependent bandgaps that increases the spectrum of useful photons.
Twisted van der Waals' Bilayers can be achieved with a range of materials (e.g. graphene carbon nitride, gallium sulfide). The materials explicitly explored are Carbon/Boron Nitride (CBN) monolayers synthesized with photolithography. To clearly exhibit the Moiré Pattern, the second layer was rotated by 2.5o. This rotation creates a periodic map of bandgaps over the material. There are distinct gradients and minima that can be used to funnel excitons. For twisted bilayer CBN (tbCBN) these bandgaps ranged from 0.53eV to 1.06eV. This range of bandgaps broadens the useful spectrum for optoelectronics. For example, a traditional photovoltaic cell has one band gap and only photons of that energy are completely absorbed. Therefore, by creating a map of bandgaps across the absorption surface spectrum loss is reduced and the cell is more efficient. By changing the material and degree of rotation, the bandgap map can be tuned to have specific properties.
A range of bandgaps over one material
Increases efficiency for optoelectronics