Unlocking new materials
Materials scientists have long known that layering can be a formula for magic, and the same is true for nanomaterials. Here, Mar Garcia Hernandez, work package leader at the Graphene Flagship explains the potential of experimenting with graphene and related materials (GRMs).
Originally - before realising the potential of graphene and related materials (GRMs), the term was used to describe single layer nanomaterials that could be integrated with graphene.
The term graphene describes a single monolayer of graphite. Tightly bound in a hexagonal honeycomb structure, these carbon layers are just one atom in height.
Hailed as the first ever two-dimensional crystal, graphene is considered a super-material because of its unrivalled strength, conductivity and light weight. Graphene, in spite of all the publicity surrounding it, is not the only single layer material with exceptional properties.
Graphene’s isolation paved the way for a new class of crystals to be discovered, all of which are one atom thick. In fact, researchers at the Graphene Flagship, one of the largest research projects funded by the European Commission, have now identified between 2,000 and 5,000 new materials that can be exfoliated to a single monolayer. While these GRMs may not boast the exact properties of graphene, combining these materials has potential for new materials solutions.
Due to their atom-scale structure, GRMs can be shuffled with each other to engineer new materials on demand. The integration of GRMs in perovskite solar cells are a good example of this.
Perovskite cells, a material increasingly used in solar panels, are most effective for power generation when used in small areas. However, large scale perovskite operations have difficultly consistently depositing solar cell layers, leading to reduced energy generation and difficulties scaling up this technology.
In a Graphene Flagship project, two different GRMs were added to perovskite cells to boost the connectivity between the perovskite and the electron-collecting titanium dioxide (TiO2) layer. This was achieved by mixing graphene flakes into the TiO2 layer and adding a separate sheet of lithium-reduced graphene oxide between the perovskite and the TiO2.
Introducing these GRMs enabled record-breaking renewable power generation for the cells, achieving a 12.6% conversion rate. Layering is a more complex process than it may appear, however. Researchers are working with different parameters while piling up layers. Among them, the angle conformed between the atomic arrangements of the various layers is of paramount importance to set the materials’ properties. This follows a discovery made in 2018, which identified that graphene could become a non-resistive superconductor when successfully twisted at a 1.1-degree angle.
When attempting the experiment, scientists discovered that the smallest error in alignment could give entirely different results. For GRMs, this means that twisting each atom layer has the potential to lead to a huge number of new materials.
Graphene Flagship research has already identified numerous possibilities for GRM structures and manipulations, the results of which are already playing functional roles in industrial applications.