Dr N. Robertson

Dyes for Solar Cells

Conducting and Magnetic Materials

Conducting Materials

Molecular conducting materials are of increasing importance in low-cost electronic devices such as transistors, light-emitting displays and solar cells. We carry out the synthesis of new small molecules for conducting materials, characterisation of their molecular properties and their study in devices, thin films and crystalline materials. The molecules studied include transition metal complexes and organic molecules.

Metal Dithiolenes

Metal dithiolene complexes (fig. 1) can show several redox processes and strong intermolecular interactions. This allows cooperative electronic behaviour over the material and control of doping leads to semiconductors or metallic conductivity.

Fig. 1: R = alkyl, thioalkyl, aromatic, etc; M = Ni, Pd, Pt, Fe, Co, Au

We use several strategies for the preparation of conducting materials from these (i) Growth of single-crystalline materials for fundamental studies (e.g. Fig. 2a) (ii) Drop or spin coating onto a substrate (e.g. Fig. 2b) (iii) Electropolymerisation through attached side groups (R = thiophene, indole).

Fig. 2: (a) stacked [Ni(dmit)2] complexes in a conducting crystal. (b) A soluble, neutral Ni-dithiolene complex

Indole Trimers

We have prepared a series of substituted, symmetric indole trimers (e.g. Fig. 3) and are studying these as semiconducting materials in field-effect transistors and as precursors for liquid-crystalline materials. The molecules possess a number of attractive features: extended planar core for strong pi-pi interactions, redox active, light-emissive and readily functionalised to alter electronic or processing properties.

Fig. 3: Example indole trimer and its X-ray structure showing pi-stacking.

Selected Recent References

Magnetic Materials

Our interest in magnetic measurements of molecular materials has two main goals:

(i) As an additional, powerful characterisation tool to extend the understanding of materials such as the dithiolene complexes described above and related metal complexes (including collaboration with P. Kyritisis, Athens).

(ii) For the study of model magnetic materials to extend the understanding of metal-metal interactions and the interaction between different functional subunits in molecular solids. This includes the use of combined high-pressure magnetisation measurements and high-pressure single-crystal diffraction to follow the structure and property changes of magnetic materials induced by altering pressure (Fig. 4).

Fig. 4: Crystal structure and change in magnetic susceptibility under pressure for the salt [TMA][MnCl3]

Selected Recent References