ChargeFabrica: An open-source simulation tool that aims to accelerate search for high performance perovskite solar cells

Perovskite solar cells (PSCs) have emerged as promising alternative for next generation photovoltaics due to their superior power conversion efficiencies (record currently at 34.9% for perovskite-silicon tandem) and low-cost manufacturing. One fully-printable implementation of perovskite solar cells uses mesoporous layers. However, the complex mesoporous architectures present a significant challenge for accurate modelling, especially considering the enhanced interfacial effects. Then, the influence of the manufacturing texturing on the charge extraction and corresponding device performance remains poorly understood. To address these limitations, a research team from Zurich University of Applied Science, ETH Zurich and École Polytechnique Fédérale de Lausanne has developed ChargeFabrica, Python-based 2D electro-ionic drift-diffusion simulator. This tool enables detailed analysis of charge and ion dynamics within complex geometries, providing insights unattainable with traditional 1D models. The platform successfully replicates experimental trends, such as thickness-dependent current–voltage characteristics and ionic pre-bias effects, paving the way for optimized device design and enhanced stability.

Perovskite solar cells have garnered worldwide attention for reaching record efficiencies with potentially simple and inexpensive fabrication methods. Despite rapid progress, several obstacles hinder their commercialization. Notably, their intricate mesoporous structures and mobile ionic species complicate the understanding of charge transport and degradation mechanisms. Existing modelling approaches, including 1D drift-diffusion simulations or commercial software, struggle to accurately simulate the lateral and interfacial phenomena inherent in mesoporous architectures. These limitations impede the precise prediction of device behaviour under operational conditions, delaying further advancements.

In general, traditional models often assume oversimplified, planar geometries, neglecting the impact of complex morphology and resulting lateral electronic and ionic movements, which are critical to device performance and stability. On the other hand, computationally intensive 3D simulations exist but are often proprietary and inaccessible to the wider research community, restricting collaborative progress.

The Solution: To fill this gap, a research team from Zürich university of applied sciences (ZHAW), ETH Zurich and École Polytechnique Fédérale de Lausanne (EPFL) has developed ChargeFabrica. This is a sophisticated, open-source simulation framework developed in Python that models mesoporous perovskite solar cells in two dimensions using finite difference methods. It can directly predict perovskite solar cell performance, including the influence of ion-displacement, using observed scanning electron microscope (SEM) geometries as a reference. Such simulations are very challenging to run as they rely on solving strongly coupled partial differential equations (PDE’s) describing the charge motion and corresponding electrostatic response using an iterative process, requiring significant processing power. To test the tool, a sponge-like scaffold consisting of   and  nanoparticles with infiltrated perovskite used in mesoporous perovskite solar cells was imaged in the SEM and used to directly model the charge transport properties in 2D. The researchers discovered that greater than 40% of the experimentally observed efficiency can be linked to geometry. This performance advantage is found to be due to the beneficial localised electron collection by the  scaffold structure that cannot be described using 1D modelling. The mobile ions are responsible for electric field screening within the structure which forces the electronic charge carriers to move via slow diffusive processes. Having short collection distances introduced via the geometry will therefore significantly reduce parasitic recombination losses.

The Future: Consequently, there could be many instances where macroscopic beneficial performance directly emerges from the micro and nanostructure employed during manufacturing. Furthermore, different perovskite materials with intrinsically higher defect density could also significantly benefit from such a mesoporous device architecture. Similar geometric properties are likely also present in plasmonic perovskite, structured tandem, mesoscopic NIP and bulk heterojunction solar cells and could be explored in the future.

The Impact: ChargeFabrica enables researchers to rapidly simulate varying geometries observed in experiments and shines a new perspective on the precise mechanism of action of mesoporous solar cells.

The research has been recently published in the online edition of Materials Futures, a prominent international journal in the field of interdisciplinary materials science research.

The ChargeFabrica GitHub repository is available at https://github.com/nsdt-zhaw/ChargeFabrica

Reference:Tristan Sachsenweger, Miguel A. Torre Cachafeiro, Wolfgang Tress. ChargeFabrica: A Python-based Finite Difference Multidimensional Electro-Ionic Drift Diffusion Simulator applied to Mesoporous Perovskite Solar Cells[J]. Materials Futures. DOI: 10.1088/2752-5724/ae27e9