Scientific Challenge leader: Francesco Buonocore
Advanced materials can contribute to the reduction in cost, increase in performance and extension of lifetime of the low-carbon energy technologies such as batteries, supercapacitors and solar cells. Thus, there is an urgent need for multi-functional and sustainable materials designed to provide a specific function in the final product. HPC can speed-up the entire process needed to identify new materials and to optimize them for the final use (Materials Roadmap). In particular, the design of advanced materials needs to consider atomic-scale chemistry and how it affects the physical properties at larger scales till the device. The Energy Materials objective in EoCoE-II will focus on three specific flagship applications in energy storage and production respectively: libNEGF (high efficiency silicon solar cells), Metalwalls (supercapacitor modelling) and KMC/DMC (organic/perovskite photovoltaics).
In order to pursue this objective, the Materials for Energy Scientific challenge is divided in three main tasks:
Shedding light on carrier dynamics at hetero-interfaces in silicon solar cells (libNEGF).
Team: Sebastian Achilles, Irene Aguilera, Francesco Buonocore, Massimo Celino, Edoardo Di Napoli, Pablo Luis Garcia-Muller, Rafael Mayo-Garcia, Simone Giusepponi, Alessandro Pecchia, Gabriele Penazzi.
This task highlights the scientific objectives and roadmap for optimizing silicon solar cells to increase in performance and extension of lifetime. Amorphous-crystalline heterointerfaces play a crucial role in the photovoltaic operation of silicon heterojunction (SHJ) technology, but the microscopic mechanisms of transport and recombination mechanisms at the interface are still poorly understood. The purpose of the present task is to understand the transport mechanisms underlying photovoltaic devices based on SHJ technology by simulating at atomistic resolution amorphouscrystalline heterointerfaces. Medium and large c-Si/a-Si:H interface models will be build up from classic molecular dynamics (MD) simulations and first-principles calculations. Ab initio electronic properties of the c-Si/a-Si:H interfaces will be calculated. Starting from the first-principles calculations, tight-binding Hamiltonians will be represented in a basis of localized Wannier functions. Next, non-equilibrium Green’s functions (NEGF) formalism will be used to analyse the effect of interfaces on the carrier transport and dynamics in silicon solar cells. Electron-photon and electronphonon scattering processes will be taken into account.
Harvesting electricity from salinity or temperature gradient (Metalwalls).
Team: Stefano Mossa, Carlo Pierleoni, Michele Ruggeri, Mathieu Salanne.
This task focuses on optimizing capacitive blue energy electrodes and thermo-electrochemical devices. Electric power production from salinity gradients harvests the free energy lost during the mixing of river with sea water in estuaries. The main technologies developed for this purpose to date exploit the electric potential differences applied across membranes, but another approach based on capacitive mixing was recently proposed. The first objective of this project will be to ascertain the best electrode structure which optimizes such a blue energy production. Thermo-electrochemical devices employ the variation of the redox potential of an active species with temperature to convert a gradient into electricity. Ionic liquids were recently proposed as optimal media for performing such an energy harvesting, and the second objective of this task will be to find compositions that will enable optimal performances. In both cases, a fundamental understanding of the cation and anion adsorption at the surface of the electrodes is essential. The challenge for this task is that simulating the interfaces requires the rigorous accounting for the interactions between the atoms of the electrodes and the adsorbed species. Due to the large size of the simulated systems for the final application, it is not possible to use electronic density functional theory (DFT) for such calculations. We therefore aim at developing new force fields for classical molecular simulations. The parameterization of these force fields can be made based on a series of electronic DFT calculations. However, it was shown recently that the commonly used exchange-correlation functionals may yield very different results for the adsorption energy of the molecules. We will overcome this problem by performing a series of Quantum Monte Carlo (QMC) reference calculations in order to benchmark them on the adsorption energies. Once the DFT functional is benchmarked on the QMC reference, a large amount of calculations will be performed to fine-tune force fields for classical molecular simulations with Metalwalls/MDFT codes. These two codes aim at simulating electrochemical systems with explicit electrodes, using either molecular dynamics or classical density functional theory to sample the configurational space of the solvent.
Organic and Perovskite solar cells (Bath-KMC/DMC).
Team: William Saunders, Alison Walker, Matthew Wolf.
This task deals with the development of a flexible and modular scheme for the multiscale modelling of electronic and ionic transport in materials for next generation photovoltaic devices. This will be built on (augmented versions of) pre-existing, MPI parallelised Python frameworks, namely Firedrake and PPMD. The scientific goals of this project, as stated in the EoCoE proposal, are:
– simulate organic photovoltaic cells of 10 nm size and study interfaces on the nm length scale to refine models of charge generation and recombination (Kinetic Monte Carlo, KMC code).
– Understand the complex processes of charge transport in a perovskite solar cell thanks to the implementation of a semiclassical approach based on solving the Boltzmann transport equation in submicron inorganic semiconductors (Device Monte Carlo, DMC code). Both KMC and DMC codes are exascale flagship codes are part of tasks in Scalable Solvers Technical Challenge of EoCoE-II