Center for Molecular Modeling - J.A. Steele

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/

Understanding the phase transition mechanism in the lead halide perovskite CsPbBr₃ via theoretical and experimental GIWAXS and Raman spectroscopy

leen — Thu, 06 Apr 2023 07:27:01 +0000

A.E.J. Hoffman, R.A. Saha, S. Borgmans, P. Puech, T. Braeckevelt, M.B.J. Roeffaers, J.A. Steele, J. Hofkens, V. Van Speybroeck

APL Materials

Volume 11, Issue 4, article number 041124

2023

Abstract

Metal-halide perovskites (MHPs) exhibit excellent properties for application in optoelectronic devices. The bottleneck for their incorporation is the lack of long-term stability such as degradation due to external conditions (heat, light, oxygen, moisture, and mechanical stress), but the occurrence of phase transitions also affects their performance. Structural phase transitions are often influenced by phonon modes. Hence, an insight into both the structure and lattice dynamics is vital to assess the potential of MHPs. In this study, GIWAXS and Raman spectroscopy are applied, supported by density functional theory calculations, to investigate the apparent manifestation of structural phase transitions in the MHP CsPbBr₃. Macroscopically, CsPbBr₃ undergoes phase transitions between a cubic (α), tetragonal (β), and orthorhombic (γ) phase with decreasing temperature. However, microscopically, it has been argued that only the γ phase exists, while the other phases exist as averages over length and time scales within distinct temperature ranges. Here, direct proof is provided for this conjecture by analyzing both theoretical diffraction patterns and the evolution of the tilting angle of the PbBr₆ octahedra from molecular dynamics simulations. Moreover, sound agreement between experimental and theoretical Raman spectra allowed to identify the Raman active phonon modes and to investigate their frequency as a function of temperature. As such, this work increases the understanding of the structure and lattice dynamics of CsPbBr₃ and similar MHPs.

Gold Open Access

DOI

http://dx.doi.org/10.1063/5.0144344

Private attachment

041124_1_5.0144344.pdf

An embedded interfacial network stabilizes inorganic CsPbI3 perovskite thin films

tbraeckevelt — Wed, 07 Dec 2022 10:38:53 +0000

J.A. Steele, T. Braeckevelt, V. Prakasam, G. Degutis, H. Yuan, H. Jin, E. Solano, P. Puech, S. Basak, M.I. Pintor-Monroy, H. Van Gorp, G. Fleury, R.X. Yang, Z. Lin, H. Huang, E. Debroye, D. Chernyshov, B. Chen, M. Wei, Y. Hou, R. Gehlhaar, J. Genoe, S. De Feyter, S.M.J. Rogge, A. Walsh, E.H. Sargent, P. Yang, J. Hofkens, V. Van Speybroeck, M.B.J. Roeffaers

Nature Communications

13, 7513

2022

Abstract

The black perovskite phase of CsPbI₃ is promising for optoelectronic applications; however, it is unstable under ambient conditions, transforming within minutes into an optically inactive yellow phase, a fact that has so far prevented its widespread adoption. Here we use coarse photolithography to embed a PbI₂-based interfacial microstructure into otherwise-unstable CsPbI₃ perovskite thin films and devices. Films fitted with a tessellating microgrid are rendered resistant to moisture-triggered decay and exhibit enhanced long-term stability of the black phase (beyond 2.5 years in a dry environment), due to increasing the phase transition energy barrier and limiting the spread of potential yellow phase formation to structurally isolated domains of the grid. This stabilizing effect is readily achieved at the device level, where unencapsulated CsPbI₃ perovskite photodetectors display ambient-stable operation. These findings provide insights into the nature of phase destabilization in emerging CsPbI₃ perovskite devices and demonstrate an effective stabilization procedure which is entirely orthogonal to existing approaches.

DOI

https://doi.org/10.1038/s41467-022-35255-9

Private attachment

s41467-022-35255-9 (1).pdf

Accurately Determining the Phase Transition Temperature of CsPbI3 via Random-Phase Approximation Calculations and Phase-Transferable Machine Learning Potentials

tbraeckevelt — Sat, 11 Jun 2022 18:44:03 +0000

T. Braeckevelt, R. Goeminne, S. Vandenhaute, S. Borgmans, T. Verstraelen, J.A. Steele, M. Roeffaers, J. Hofkens, S.M.J. Rogge, V. Van Speybroeck

Chemistry of Materials

34, 19, 8561–8576

2022

Abstract

While metal halide perovskites (MHPs) have shown great potential for various optoelectronic applications, their widespread adoption in commercial photovoltaic cells or photosensors is currently restricted, given that MHPs such as CsPbI₃ and FAPbI₃ spontaneously transition to an optically inactive nonperovskite phase at ambient conditions. Herein, we put forward an accurate first-principles procedure to obtain fundamental insight into this phase stability conundrum. To this end, we computationally predict the Helmholtz free energy, composed of the electronic ground state energy and thermal corrections, as this is the fundamental quantity describing the phase stability in polymorphic materials. By adopting the random phase approximation method as a wave function-based method that intrinsically accounts for many-body electron correlation effects as a benchmark for the ground state energy, we validate the performance of different exchange-correlation functionals and dispersion methods. The thermal corrections, accessed through the vibrational density of states, are accessed through molecular dynamics simulations, using a phase-transferable machine learning potential to accurately account for the MHPs’ anharmonicity and mitigate size effects. The here proposed procedure is critically validated on CsPbI₃, which is a challenging material as its phase stability changes slowly with varying temperature. We demonstrate that our procedure is essential to reproduce the experimental transition temperature, as choosing an inadequate functional can easily miss the transition temperature by more than 100 K. These results demonstrate that the here validated methodology is ideally suited to understand how factors such as strain engineering, surface functionalization, or compositional engineering could help to phase-stabilize MHPs for targeted applications.

Open Access version available at UGent repository

Gold Open Access

DOI

https://doi.org/10.1021/acs.chemmater.2c01508

Private attachment

acs.chemmater.2c01508.pdf

Texture Formation in Polycrystalline Thin Films of All-Inorganic Lead Halide Perovskite

sven — Sat, 16 Jan 2021 12:42:12 +0000

J.A. Steele, E. Solano, H. Jin, V. Prakasam, T. Braeckevelt, H. Yuan, Z. Lin, R. de Kloe, Q. Wang, S.M.J. Rogge, V. Van Speybroeck, D. Chernyshov, J. Hofkens, M. Roeffaers

Advanced Materials

33 (13), 2007224

2021

Abstract

Controlling grain orientations within polycrystalline all-inorganic halide perovskite solar cells can help increase conversion efficiencies toward their thermodynamic limits, however the forces governing texture formation are ambiguous. Using synchrotron X-ray diffraction, we report meso-structure formation within polycrystalline CsPbI_2.85Br_0.15 powders as they cool from a high-temperature cubic perovskite (α-phase). Tetragonal distortions (β-phase) trigger preferential crystallographic alignment within polycrystalline ensembles, a feature we suggest is coordinated across multiple neighboring grains via interfacial forces that select for certain lattice distortions over others. External anisotropy is then imposed on polycrystalline thin films of orthorhombic (γ-phase) CsPbI_3-xBr_x perovskite via substrate clamping, revealing two fundamental uniaxial texture formations; (i) I-rich films possess orthorhombic-like texture (<100> out-of-plane; <010> and <001> in-plane), while (ii) Br-rich films form tetragonal-like texture (<110> out-of-plane; <1-10> and <001> in-plane). In contrast to relatively uninfluential factors like the choice of substrate, film thickness and annealing temperature, Br incorporation modifies the γ-CsPbI_3-xBr_x crystal structure by reducing the orthorhombic lattice distortion (making it more tetragonal-like) and governs the formation of the different, energetically favored textures within polycrystalline thin films.

DOI

http://dx.doi.org/10.1002/adma.202007224

Thermal unequilibrium of strained black CsPbI3 thin films

sven — Thu, 25 Jul 2019 18:07:18 +0000

J.A. Steele, H. Jin, I. Dovgaliuk, R.F. Berger, T. Braeckevelt, H. Yuan, C. Martin, E. Solano, K. Lejaeghere, S.M.J. Rogge, C. Notebaert, W. Vandezande, K.P.F. Janssen, B. Goderis, E. Debroye, Y.-K. Wang, Y. Dong, D. Ma, M. Saidaminov, H. Tan, Z. Lu, V. Dyadkin, D. Chernyshov, V. Van Speybroeck, E.H. Sargent, J. Hofkens, M. Roeffaers

Science

365 (6454), 679-684

2019

Abstract

The high-temperature all-inorganic CsPbI₃ perovskite black phase is metastable relative to its yellow non-perovskite phase, at room temperature. Since only the black phase is optically active, this represents an impediment for the use of CsPbI₃ in optoelectronic devices. We report the use of substrate clamping and biaxial strain to render stable, at room temperature, black phase CsPbI₃ thin films. We used synchrotron-based grazing incidence wide angle x-ray scattering to track the introduction of crystal distortions and strain-driven texture formation within black CsPbI₃ thin films when they were cooled following annealing at 330°C. The thermal stability of black CsPbI₃ thin films is vastly improved by the strained interface, a response verified by ab initio thermodynamic modelling.

Open Access version available at UGent repository

Gold Open Access

DOI

http://dx.doi.org/10.1126/science.aax3878

Private attachment

science.aax3878.full_.pdf

Accurately determining the transition temperature of metal halide perovskites via RPA calculations and phase-transferable machine learning potentials

tbraeckevelt — Thu, 07 Jul 2022 11:37:18 +0000

T. Braeckevelt, R. Goeminne, S. Vandenhaute, S. Borgmans, T. Verstraelen, J.A. Steele, M. Roeffaers, J. Hofkens, S.M.J. Rogge, V. Van Speybroeck

ISBN/ISSN:

Talk

Conference / event / venue

DFT2022

Brussels, Belgium

Monday, 29 August, 2022 to Friday, 2 September, 2022

Abstract (private)

Braeckevelt_abstract.pdf

Stabilizing the perovskite phase of cesium lead iodide thin films via interfacial strains

tbraeckevelt — Sun, 19 Jan 2020 14:46:54 +0000

T. Braeckevelt, J.A. Steele, K. Lejaeghere, S.M.J. Rogge, M. Roeffaers, J. Hofkens, V. Van Speybroeck

ISBN/ISSN:

Poster

Conference / event / venue

MolSim-2020: Understanding Molecular Simulation

Amsterdam, The Netherlands

Monday, 6 January, 2020 to Friday, 17 January, 2020

Stabilizing the perovskite phase of cesium lead iodide thin films via interfacial strains

tbraeckevelt — Sun, 19 Jan 2020 14:43:28 +0000

T. Braeckevelt, J.A. Steele, K. Lejaeghere, S.M.J. Rogge, M. Roeffaers, J. Hofkens, V. Van Speybroeck

ISBN/ISSN:

Poster

Conference / event / venue

5th International Conference on Perovskite Solar Cells and Optoelectronics (PSCO19)

Lausanne, Switzerland

Monday, 30 September, 2019 to Wednesday, 2 October, 2019

Stabilizing the perovskite phase of cesium lead iodide thin films via interfacial strains

tbraeckevelt — Sun, 19 Jan 2020 14:38:11 +0000

T. Braeckevelt, J.A. Steele, K. Lejaeghere, S.M.J. Rogge, M. Roeffaers, J. Hofkens, V. Van Speybroeck

ISBN/ISSN:

Poster

Conference / event / venue

ICAMM conference

Rennes, France

Monday, 1 July, 2019 to Wednesday, 3 July, 2019