Materials Discovery in Charge Transfer Complexes for Thermoelectricity

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Thermoelectric devices are electronic chips that turn differences in heat into electricity and vice versa. Most people will have never heard of thermoelectric (TE) devices as they are used very little. Practical TE devices could generate green electricity and make refrigeration less polluting. This cant happen currently as room temperature thermoelectric materials are either too expensive or too inefficient. A 1.4% efficient TE material applied to the 40C waste steam generated by all UK thermal power plants in 2021 could have generated 5TWh of electricity per year, enough for 2 million, 8% of all, UK homes at a wholesale value of £900M per year (UK average price June 22 June 23). Organic TE materials are likely to reduce the cost of TE devices due to their atom abundance and low energy processing. Both negative and positive type (like the ends on a battery) TE materials are needed to make devices. Organic p-type materials have seen good progress, but n-types are much rarer, have lower performance, and are easily decomposed by oxidation in air. A recent discovery of a family of metal halide organic complexes with a generic structure M(II)Br2(Haloaniline)2 has reported high (2000-3900 S cm-1) electrical conductivity and power factors, a measure of TE performance (1500 3700 W m1 K2) an order of magnitude greater than the research benchmark of PEDOT:PSS polymer 200 W m1 K2.This new family's constituent atoms are all earth-abundant, comprised of Cu, Zn, Br, I, C and N.Currently, the processing solvent is toxic, but there is potential for developing safer and less environmentally harmful solvent methods. Crucially, this family reports high stability in air and water for year timescales experimentally and theoretically. And maximum operating temperatures between 100 - 200C and good performance one-fifth to half as good as the best materials available. This class of materials is underexplored as TE materials, and many questions about how to boost their performance remain. This project will help to develop methods for their production, discover new materials in the family and explore methods for tailoring their performance. The early goal will be to replicate the leading research results via vacuum drying. If this method reliably gives films that can be analysed, then a library of different organic molecules with different halide substituents and Pi-conjugated systems will be developed. These experiments will help us understand the molecule's effect on how we can make the materials better. If data generation is fast and reliable, the use of artificial intelligence could help us improve the materials. If the vacuum drying technique does not provide reliable deposition of high-quality films, then alternative drying methods will be investigated. Hot substrates to evaporate off the solvent, using a solvent that washes away the solvent but leaves the materials in place. Ambient temperature washing is favourable as it avoids thermal stress and has lower energy requirements. Cosolvent techniques may give finer control of the crystallisation. Once films are produced, they will be validated for homogeneity and thickness with Optical microscopy, Electron microscopy, and profilometry. The composition of the deposited films will be determined by grazing incidence x-ray diffraction. Previous studies have not included structural measurements of the cast films, only materials derived by mechanochemistry and crystallisation. Analysis of the cast film will reveal any differences. If possible, the materials will be cast onto the silicon nitride measurement chips of a thin film analyser. This system can give basic thermoelectric characterisation. This system's speed and high reliability will reduce uncertainty and time per sample compared to conventional measurements. If this system is unsuitable, methods will be developed using silica slides with thermally evaporated conductive tracks for 4 terminal measurements.