The development of advanced materials for applications in rechargeable batteries, supercapacitors, solar cells and photocatalysts is the key to accelerating the uptake of renewable energy technologies. First principles methods that predict the structure and properties of materials using quantum mechanics are playing an increasingly important role in materials discovery and optimisation in this field. However, real materials are not perfect. They are often structured at the nanoscale and contain a range of extended defects (such as grain boundaries) which affect performance. This project aims to develop and apply theoretical approaches mainly based on density functional theory (DFT) to model the structural, thermodynamic and electronic properties of extended defects in a range of polycrystalline energy materials in order to understand their impact on performance and guide the optimisation of materials.

The initial stage of the project (year 1) will focus on understanding the role of grain boundaries in barium titanate (BTO) thin films with relevance to multilayer supercapacitors which find application for efficient on-chip energy storage for mobile electronics and personal computers. In particular, the structure and electronic properties of grain boundary (GB) defects in BTO [specifically (111) and (310) GBs] will be investigated using DFT and the gamma surface method as described in previous work in the group [e.g. K. P. McKenna, ACS Energy Letters 3, 2663 (2018)]. The modulation of electronic properties due to the presence of GB defects as well as associated segregation of intrinsic point defect such as vacancies will be studied. The project will also investigate the role that ferroelectric polarisation plays on GB properties. There will be close interaction with experimental collaborators to test predictions and validate results. The groups of M. Nafria (University of Barcelona) and G. Bersuker (Aerospace Corp., USA) will provide experimental conductive AFM mapping on polycrystalline BTO films to compare to the theoretical predictions.

In years 2 and 3 the student will build on the experience, methods and skills developed in year 1 to model grain boundaries in other energy materials, again with close interaction with experimental collaborators to test predictions and validate results. We plan to study the effect of grain boundaries on recombination in next generation solar absorber materials (Sb2Se3 and related materials) in collaboration with K. Durose, Jon Major and Tim Veal (University of Liverpool) and the role of grain boundaries in limiting mobility in fluorine doped tin oxide, a widely used transparent conductor for photovoltaics applications. We will retain some flexibility in the project to tackle emerging materials of topical interest particularly where there new experimental data becomes available that could be better understood by modelling extended defects.