Center for Molecular Modeling - S. Bals

Generating a Stable Higher-Symmetry CsPbI3 Perovskite Phase in Ambient Conditions: Unveiling the Stabilization Mechanism

tbraeckevelt — Mon, 26 Jan 2026 12:20:59 +0000

R.A. Saha, A. Papadopoulou, R. Ariza, G. Degutis, I. Skvortsova, T. Braeckevelt, F. De Angelis, E. Solano, J. P. de Sousa Gouveia dos Anjos, M. I. Pintor Monroy, I. Mongilyov, B. God, J. Rubio-Zuazo, J. Genoe, C. Meneghini, J.A. Steele, S. Bals, V. Van Speybroeck, J. Hofkens

ACS Nano

19, 31, 28540–28553

2025

Abstract

Black-phase cesium lead iodide (CsPbI₃) is a promising candidate for high-efficiency perovskite optoelectronics, but its instability under ambient conditions remains a major challenge. Among several strategies, dimethylammonium iodide (DMAI) has emerged as a potential stabilizer; however, inconsistencies in phase stability (3–7 days) and lower solar power conversion efficiencies (∼20 vs ∼27% for hybrid perovskites) highlight the need for further improvements. This study not only demonstrates enhanced stabilization of the high-symmetry black phase of CsPbI₃ and improved film morphology through optimized composition and annealing conditions but also more importantly provides detailed mechanistic insights obtained from comprehensive experimental and theoretical analyses. Systematic tuning of the DMAI concentration (1.2 M), annealing temperature (200 °C, 1 min), and Cs⁺ substitution (12–15%) significantly extends phase stability to 7 days under ambient conditions (35–52% relative humidity) and maintains stability even after 16 months in a drybox environment by reducing orthorhombic strain and octahedral tilting. Additionally, a minor (∼5%) zero-dimensional (0D) Cs₄PbI₆ phase fills pinholes, enhancing the film quality. Optimized photodiodes exhibit a low dark current (∼1 μA/cm²), high external quantum efficiency (∼80% at −2 V), and a ≥100 dB linear dynamic range. These findings provide mechanistic insights into the stabilization of the black phase of CsPbI₃, advancing the development of more stable and efficient perovskite-based optoelectronic devices.

DOI

http://dx.doi.org/

Increasing the Phase Stability of CsPbI3 Nanocrystals by Zn2+ and Cd2+ Addition: Synergy of Transmission Electron Microscopy and Molecular Dynamics

leen — Thu, 26 Jun 2025 11:39:11 +0000

I. Skvortsova, T. Braeckevelt, A. De Backer, N. Schrenker, B. Pradhan, J. Hofkens, S. Van Aert, V. Van Speybroeck, S. Bals

ACS Nano

19, 18, 17698-17708

2025

Abstract

Metal halide perovskites (MHPs) are emerging as promising materials for optoelectronic and photovoltaic applications due to their favorable electronic properties, including a tunable bandgap. However, achieving high stability for these materials remains a critical challenge, particularly for CsPbI₃, whose photoactive phases spontaneously convert into a nonphotoactive yellow orthorhombic δ-phase under ambient conditions. This transformation results in a significant increase in bandgap and a loss of photoactive functionality. In this study, we investigate the impact of Zn²⁺ and Cd²⁺ dopants on the phase stability of CsPbI₃ nanocrystals (NCs), emphasizing the formation of Ruddlesden–Popper (RP) planar defects, which are frequently observed during compositional tuning. Using transmission electron microscopy (TEM), we follow the temporal evolution of the phase transformation, where black-phase NCs agglomerate and form elongated microtubes with a yellow-phase crystal structure. Our observations demonstrate that doped samples are significantly more stable, while the dopants are key factors in the formation of the RP-like defects with specific atomic arrangements. Using a combination of quantitative TEM and molecular dynamics (MD) simulations we characterize the structure and composition of as-found RP-like defects and elucidate their role in stabilizing the photoactive phases of CsPbI₃ through decreased phase transition kinetics.

DOI

http://dx.doi.org/10.1021/acsnano.5c01825

Private attachment

skvortsova-et-al-2025-increasing-the-phase-stability-of-cspbi3-nanocrystals-by-zn2-and-cd2-addition-synergy-of.pdf

Investigation of the Octahedral Network Structure in Formamidinium Lead Bromide Nanocrystals by Low-Dose Scanning Transmission Electron Microscopy

leen — Thu, 22 Aug 2024 09:05:30 +0000

N. J. Schrenker, T. Braeckevelt, A. De Backer, N. Livakas, C.-P. Yu, T. Friedrich, M.B.J. Roeffaers, J. Hofkens, J. Verbeeck, L. Manna, V. Van Speybroeck, S. Van Aert, S. Bals

Nano Letters

24, 35, 10936-10942

2024

Abstract

Metal halide perovskites (MHP) are highly promising semiconductors. In this study, we focus on FAPbBr₃ nanocrystals, which are of great interest for green light-emitting diodes. Structural parameters significantly impact the properties of MHPs and are linked to phase instability, which hampers long-term applications. Clearly, there is a need for local and precise characterization techniques at the atomic scale, such as transmission electron microscopy. Because of the high electron beam sensitivity of MHPs, these investigations are extremely challenging. Here, we applied a low-dose method based on four-dimensional scanning transmission electron microscopy. We quantified the observed elongation of the projections of the Br atomic columns, suggesting an alternation in the position of the Br atoms perpendicular to the Pb–Br–Pb bonds. Together with molecular dynamics simulations, these results remarkably reveal local distortions in an on-average cubic structure. Additionally, this study provides an approach to prospectively investigating the fundamental degradation mechanisms of MHPs.

This publication is licensed under the terms of your institutional subscription. Request reuse permissions.

DOI

https://doi.org/10.1021/acs.nanolett.4c02811

Private attachment

schrenker-et-al-2024-investigation-of-the-octahedral-network-structure.pdf

Additivity of atomic strain fields as a tool to strain-engineering phase-stabilized CsPbI3 perovskites

leen — Mon, 13 Nov 2023 10:15:01 +0000

J. Teunissen, T. Braeckevelt, I. Skvortsova, J. Guo, B. Pradhan, E. Debroye, M. Roeffaers, J. Hofkens, S. Van Aert, S. Bals, S.M.J. Rogge, V. Van Speybroeck

The Journal of Physical Chemistry C

127, 48, 23400-23411

2023

Abstract

CsPbI₃ is a promising perovskite material for photovoltaic applications in its photoactive perovskite or black phase. However, the material degrades to a photovoltaically inactive or yellow phase at room temperature. Various mitigation strategies are currently being developed to increase the lifetime of the black phase, many of which rely on inducing strains in the material that hinder the black-to-yellow phase transition. Physical insight into how these strategies exactly induce strain as well as knowledge of the spatial extent over which these strains impact the material is crucial to optimize these approaches but is still lacking. Herein, we combine machine learning potential-based molecular dynamics simulations with our in silico strain engineering approach to accurately quantify strained large-scale atomic structures on a nanosecond time scale. To this end, we first model the strain fields introduced by atomic substitutions as they form the most elementary strain sources. We demonstrate that the magnitude of the induced strain fields decays exponentially with the distance from the strain source, following a decay rate that is largely independent of the specific substitution. Second, we show that the total strain field induced by multiple strain sources can be predicted to an excellent approximation by summing the strain fields of each individual source. Finally, through a case study, we illustrate how this additive character allows us to explain how complex strain fields, induced by spatially extended strain sources, can be predicted by adequately combining the strain fields caused by local strain sources. Hence, the strain additivity proposed here can be adopted to further our insight into the complex strain behavior in perovskites and to design strain from the atomic level onward to enhance their sought-after phase stability.

Open Access version available at UGent repository

Gold Open Access

DOI

http://dx.doi.org/10.1021/acs.jpcc.3c05770

Private attachment

teunissen-et-al-2023-additivity-of-atomic-strain-fields-as-a-tool-to-strain-engineering-phase-stabilized-cspbi3.pdf

Catalytic and molecular separation properties of Zeogrids and Zeotiles

wim — Mon, 22 Aug 2011 14:08:06 +0000

J.A. Martens, J.W. Thybaut, J.F.M. Denayer, S. Pulinthanathu Sree, A. Aerts, M-F. Reyniers, V. Van Speybroeck, M. Waroquier, A. Buekenhoudt, I. Vankelecom, W. Buijs, J. Persoons, G.V. Baron, S. Bals, G. Van Tendeloo, G.B. Marin, P.A. Jacobs, C. Kirschhock

Catalysis Today

168, 17-27

2011

Abstract

Zeogrids and Zeotiles are hierarchical materials built from assembled MFI zeolite precursor units. Permanent secondary porosity in these materials is obtained through self assembly of nanoparticles encountered in MFI zeolite synthesis in the presence of supramolecular templates. Hereon, the aggregated species are termed nanoslabs. Zeogrids are layered materials with lateral spacings between nanoslabs creating galleries qualifying as supermicropores. Zeotiles present a diversity of tridimensional nanoslab assemblies with mesopores. Zeotile-1, -4 and -6 are hexagonal mesostructures. Zeotile-1 has triangular and hexagonal channels; Zeotile-4 has hexagonal channels interconnected via slits. Zeotile-2 has a cubic structure with gyroid type mesoporosity. The behavior of Zeogrids and Zeotiles in adsorption, membrane and chromatographic separation and catalysis has been characterized and compared with zeolites and mesoporous materials derived from unstructured silica sources. Shape selectivity was detected via adsorption of n- and iso-alkanes. The mesoporosity of Zeotiles can be exploited in chromatographic separation of biomolecules. Zeotiles present attractive separation properties relevant to CO2 sequestration. Because of its facile synthesis procedure without hydrothermal steps Zeogrid is convenient for membrane synthesis. The performance of Zeogrid membrane in gas separation, nanofiltration and pervaporation is reported. In the Beckmann rearrangement of cyclohexanone oxime Zeogrids and Zeotiles display a catalytic activity characteristic of silicalite-1 zeolites. Introduction of acidity and redox catalytic activity can be achieved via incorporation of Al and Ti atoms in the nanoslabs during synthesis. Zeogrids are active in hydrocracking, catalytic cracking, alkylation and epoxidation reactions. Zeogrids and Zeotiles often behave differently from ordered mesoporous materials as well as from zeolites and present a valuable extension of the family of hierarchical silicate based materials.

DOI

http://dx.doi.org/10.1016/j.cattod.2011.01.036

Private attachment

11 cat today 168,17 martens.pdf

Design of zeolite by inverse sigma transformation

wim — Mon, 12 Aug 2013 14:09:45 +0000

E. Verheyen, L. Joos, K. Van Havenbergh, E. Breynaerts, N. Kasian, E. Gobechiya, K. Houthoofd, C. Martineau, M. Hinterstein, F. Taulelle, V. Van Speybroeck, M. Waroquier, S. Bals, G. Van Tendeloo, C. Kirschhock, J.A. Martens

p. 70

ISBN/ISSN:

Talk

Conference / event / venue

IZC17

Moscow, Russia

Sunday, 7 July, 2013 to Friday, 12 July, 2013

Conference reference

IZC-17

Computational Approach of the Inverse Sigma Transformation of Zeolites

wim — Mon, 12 Aug 2013 14:07:29 +0000

p. 219

ISBN/ISSN:

Poster

Conference / event / venue

IZC17

Moscow, Russia

Sunday, 7 July, 2013 to Friday, 12 July, 2013

Conference reference

IZC-17

Design of zeolite by inverse sigma transformation

michel — Mon, 03 Sep 2012 10:08:14 +0000

E. Verheyen, L. Joos, K. Van Havenbergh, N. Kasian, E. Gobechiya, K. Houthoofd, M. Hinterstein, E. Breynaerts, V. Van Speybroeck, M. Waroquier, S. Bals, G. Van Tendeloo, C. Kirschhock, J.A. Martens

Nature Materials

11 (12), 1059-1064

2012

Abstract

Zeolites are silicon materials, that have channels and pores on the nanoscale. This paper reports the synthesis of a new zeolite, in which the pores were widened using a revolutionary synthesis method. The final material has a series of unique and special properties, useful for industrial processes. Molecular modeling was used to determine the structure of the material.

Zeolieten zijn materialen opgebouwd uit silicium, die op nanoschaal kanalen en poriën bevatten. Deze paper rapporteert de synthese van een nieuw type zeoliet, waarbij de kanalen op een revolutionaire manier werden vergroot. Het eindmateriaal heeft daarom een hele reeks aan unieke en bijzonder interessante eigenschappen voor een aantal industriële processen. Moleculaire modelering werd gebruikt om de structuur van het materiaal te bepalen.

A graphical representation of COK14:

DOI

http://dx.doi.org/10.1038/nmat3455

Private attachment

12_nat_mat_11(12)1059_Verheyen.pdf

nmat3455-s1.pdf