Research

My research interests are centred around materials used for renewable energy generation (e.g. solar cells) and storage (e.g. reusable batteries). I use a branch of physics called Density Functional Theory (DFT) to predict the properties of these materials and link the macroscopic observables (such as open circuit voltage or thermodynamic stability) with microscopic processes (such as electron capture or electron-phonon coupling).

DFT is an ab-initio method derived from quantum mechanics and can be used to predict material properties without experimental input [1]. To investigate the complex materials and processes underpinning emerging energy technologies a series of approximations are used, and so any results should be validated against experiment. Once validated, these atomic scale models can be used to guide experimental investigations - for example, to predict a new material with a particular target property.

When DFT is applied to crystalline materials it is usually assumed that there is perfect translational symmetry - that there are no defects (missing or extra atoms) - and that the atoms are perfectly static. However a material always has defects (these are unavoidable due to the laws of thermodynamics [2]), and the atomic lattice vibrates with heat. These defects and vibrations are important to understand because they can have a large impact upon the performance of a device. My previous research has focused on the Defects and Distortions in Hybrid Halide Perovskites, a family of materials that have become incredibly popular over the last decade as they can convert sunlight into electricity efficiently, and have the potential to form more flexible, lightweight and cheaper solar panels than those currently on the market.

[1] There are a number of case studies given in “Computational predictions of energy materials using density functional theory” which is available for download on ResearchGate.
[2] This is because the cost in lattice energy is balanced by the change in entropic energy. See, for example, “Defects and Defect Processes in Nonmetallic Solids”, Hayes and Stoneham, section 3.1.

Left: crystal structure of a hybrid halide perovskite; Right: hybrid halide perovskite with a halide vacancy defect