Materials Informatics for Solar Energy Conversion

My research is motivated by a desire to aid the scientific effort to mitigate and prevent the impact of the climate and ecological emergency. It is recognized that dramatic technological and societal developments are required in order to achieve this. The global energy market encompasses approximately one seventh of worldwide gross-domestic-product (GDP) and produces around seventy percent of international CO2 emissions. I believe, therefore, that the transition toward a more equitable, sustainable society must begin here.

Multiple renewable energy sources have been established. Whilst each such technology has its own merits, solar energy is the largest source and most widespread. It has the potential, therefore, to have the largest impact. Multiple solar technologies have been commercially established and are now amongst the cheapest sources to generate electricity. Despite this, next-generation solar materials which are thinner, more flexible, less energy intensive to produce, and which can be incorporated into buildings or other technologies more easily are motivated.

Halide perovskite solar cells are widely recognized as the most promising next-generation solar technology. The group of materials synthesise with chemical formula ABX3, where A is a molecular (or atomic) cation placed at the centre of a metal-halide octahedral structure. The best performing solar devices are based upon 'mixed perovskites'; lab-based devices realise a power conversion efficiency of over 24% and are stable for more than a thousand hours. As the name suggests, mixed perovskites are composed of a mixture of A and X sites, and are usually composed of; A = CH3NH3, CH(NH2)2, and Cs, and X = I .
Significant operational issues remain, however, which have limited the commercial success of these materials. These include but are not limited to: thermodynamic instability; ion conduction; J-V curve hysteresis; degradation due to hydration; phase separation; and strain/polar effects. The theoretical understanding of such processes is lacking and therefore these issues have not been mitigated.

In an attempt to improve the commercial viability of this group of materials, my work is a theoretical study focused on discerning the underlying physical mechanisms which drive the operational behaviour of perovskite based solar devices. Initially, the study will be focused on improving our understanding of the structural phase behaviour of single cation perovskite materials. Many of the device issues introduced above are dependent upon the structural phase of the material; that is to say, we cannot understand or mitigate these effects until we have a comprehensive understanding of the phase behaviour. Further calculations will be subsequently performed in order to deduce the impact on device performance of our improved structural models. This work will be extended by contemplating state-of-the-art mixed-cation perovskite systems.

I utilise a range of theoretical techniques to achieve this, including density functional theory (DFT), molecular dynamics (MD), the theory of thermodynamics, monte-carlo simultations (MC), group theory and the theory of electrostatics. The novelty of the approach relies upon the inclusion of all these theoretical techniques into a single workflow. The DFT calculations are informed by group theory. The MD simulations informed by the DFT calculations. The MC code, written using the theory of thermodynamics, is then informed by MD simulations. As a result of this workflow, this study will be able to simulate the behaviour of perovskite materials up to 1microm^3 - larger than any previous study.