Computational Materials Design of Excitonic Systems for Solar Energy ConversionResearchers from the ARC Centre of Excellence in Exciton Science (ACEx) are using the Pawsey Supercomputing Centre's resources to study the properties of advanced molecular and nano materials in order to improve our ability to harness solar energy and to create energy-efficient devices.
The ARC Centre of Excellence in Exciton Science seeks to understand how photons interact with advanced molecular and nano materials in order to improve the way that we harness and use light energy, with particular focus on new materials for harnessing the full spectrum of light and the development of novel hybrid materials that will improve our ability to manipulate light. This requires a joint experimental and theoretical effort, with access to high-power computing facilities that can support a broad computational materials discovery program as well as more focused studies of complex phenomena across a wide range of length and time scales, ranging from the energetics and dynamics of electrons, molecules and colloids, right up to whole device scales.
Pawsey’s petascale capability allows us to carry out a wide range of challenging calculations that simply would not be practical with smaller facilities. This includes quantum mechanical calculations of excited electronic states in molecular chromophores, nanoparticles, and coupled systems, which can require TBs of memory; and large-scale molecular dynamics simulations of 100,000s of atoms for 100s of ns, in order to understand the forces that keep nanoparticle inks stable, or the complex processes involved in the formation of printable solar cells. The efficient highly parallel processing available on the Magnus supercomputer at Pawsey is essential for carrying out these types of investigations.
In 2019, Magnus was used to study the formation and properties of a range of excitonic materials:
1) We characterised how tiny nanoparticles interact with one another in solution. Being able to make more concentrated nanoparticle inks and control how the particles will order when they crash out of solution is important for being able to make more efficient optoelectronic devices via scalable and low-waste printing processes. One particularly important class of nanoparticles are inorganic cores coated with a layer of hair-like molecules. This outer ligand layer is essential for keeping the particles from randomly aggregating in solution but can affect the particle stability in ways that cannot be explained using existing theories. Using a combination of experimental and theoretical work, we examined why the stability of nanoparticle dispersions can be strongly affected by subtle changes to the structure of ligand and solvent molecules. The insights obtained from this work, some already published in ACS Nano , will help to create more stable nanoparticle dispersions for a range of applications.
2) We developed and evaluated force fields for studying the formation and dissolution of metal halide perovskites , a key component in a class of printable solar cells that could revolutionise our transition to renewable energy. Metal halide perovskites are inorganic or organometallic materials that can be formed into thin crystalline films by depositing a solution of precursor ions onto a substrate and then removing the solvent. This process has been used to make very efficient perovskite solar cells (PSCs) at small scale, however there are barriers to converting this success into a mature technology. For example, PSCs are not as stable under humid environmental conditions as conventional silicon-based solar cells, and it is not currently possible to print efficient PSCs at scale. One of the central problems is that we lack a detailed understanding of how perovskite crystals form at the molecular level and of how to influence this process. The work carried out in 2019 will make it easier to tackle this problem using computational modelling. We also used Pawsey to understand the driving forces responsible for segregation in mixed halide perovskites, which is a major barrier to using these materials in solar cells.
3) We studied the mechanism by which rod-shaped nanoparticles can be assembled into large-scale arrays with control of both position and orientation at the nm-scale using electrophoretic deposition. This mechanism can be used to create materials with orientation-dependent optoelectronic properties, which could find application in displays, sensors and solar cells.
4) We used first-principles calculations in combination with experiments to study triplet exciton diffusion in the conducting polymer PPV , which is relevant to increasing the efficiency and range of use of solar cells; and used theoretical calculations to study enhanced light emission in small molecular aggregates .
List of Publications
1. Monego, D.; Kister, T.; Kirkwood, N.; Doblas, D.; Mulvaney, P.; Kraus, T.; Widmer-Cooper, A. “When Like Destabilizes Like: Inverted Solvent Effects in Apolar Nanoparticle Dispersions” ACS Nano 2020, 14, 5278. DOI: 10.1021/acsnano.9b03552
2. Rathnayake, P.V.G.M.; Bernardi, S.; Widmer-Cooper, A. “Evaluation of the AMOEBA force field for simulating metal halide perovskites in the solid state and in solution” J. Chem. Phys. 2020, 152, 024117. DOI: 10.1063/1.5131790
3. Lyskov, I; Trushin, E; Baragiola, B.Q.; Schmidt, T.W.; Cole, J.H.; Russo, S.P. “First-Principles Calculation of Triplet Exciton Diffusion in Crystalline Poly(p-phenylene vinylene)” J. Phys. Chem. C 2019 123, 26831. DOI: 10.1021/acs.jpcc.9b08203
4. Zhang, B; Lyskov, I; Wilson, L; Sabatini, R.P.; Manian, A; Soleimaninejad, H; White, J; Smith, T; Lakhwani, G; Jones, D.J.; Ghiggino, K; Russo, S.P.; Wong, W.W.H. “FRET-Enhanced Photoluminescence of Perylene Diimides by Combining Molecular Aggregation and Insulation” J. Mater. Chem. C 2020. DOI: 10.1039/D0TC02108C