Advances in multi-phase FAPbI<sub>3</sub> perovskite: another perspective on photo-inactive δ-phase

Junyu Li; Songwei Zhang; Mohd Nazim Mohtar; Nattha Jindapetch; Istvan Csarnovics; Mehmet Ertugrul; Zhiwei Zhao; Jing Chen; Wei Lei; Xiaobao Xu

doi:10.1088/1674-4926/24100024

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Advances in multi-phase FAPbI₃ perovskite: another perspective on photo-inactive δ-phase

Junyu Li^{1, §}, Songwei Zhang^{1, §}, Mohd Nazim Mohtar², Nattha Jindapetch³, Istvan Csarnovics⁴, Mehmet Ertugrul⁵, Zhiwei Zhao¹, Jing Chen^1,, Wei Lei^1, and Xiaobao Xu^1,

+ Author Affiliations

1. Joint International Research Laboratory of Information Display and Visualization, School of Electronic Science and Engineering, Southeast University, Nanjing 211189, China
2. MyAgeingS1, University Putra Malaysia, Serdang, Selangor 43400, Malaysia
3. Department of Electrical and Biomedical Engineering, Faculty of Engineering, Prince of Songkla University, Hat Yai, Songkhla 90110, Thailand
4. Faculty of Science and Technology, University of Debrecen, Debrecen 4026, Hungary
5. Department of Metallurgy and Material Science Engineering Composite Materials, Engineering Faculty, Karadeniz Technical University, Trabzon 61080, Turkey
^§Junyu Li and Songwei Zhang contributed equally to this work and should be considered as co-first authors.

Author Bio:

Junyu Li received his Ph.D degree from Nanjing University of Science and Technology. He is currently a postdoctoral fellow in Joint International Research Laboratory of Information Display and Visualization, school of Electronic Science and Engineering, Southeast University. His current research interests focus on functional optoelectronic devices, especially terahertz sensing based on perovskite single crystals.

Songwei Zhang is currently a master's student in Joint International Research Laboratory of Information Display and Visualization, school of Electronic Science and Engineering, Southeast University. He received his Bachelor’s degree in Electronic Science and Technology from Southeast University in 2023. His current research interests focus on perovskite X-ray detectors.

Wei Lei received his Ph.D degree from Southeast University, China in 1994. After completing his doctoral studies, he worked in the department of Electronic Science and Engineering as assistant professor, associate professor, and professor. He is mainly involved in the field of the light emitting source, display, photo detection, and X-ray/ray imaging. A few novel materials, such as quantum dots, nano crystals, and perovskite single crystal, are used to improve the performance of light emitting device and photodetectors. In recent 5 years, more than 150 scientific journal papers have been published in these fields, and about 20 patents have been granted.

Xiaobao Xu received his B.S. in Chemical Engineering and Technology and Ph.D in Optical Engineering from Huazhong University of Science and Technology in 2011 and 2016, respectively. He also studied in Prof. Yang Yang’s group (University of California, Los Angeles) as visiting student from 2014 to 2015 and worked in Prof. Alex Jen’s group (University of Washington, Seattle) as research associate from 2016−2018. Now, he works at Southeast University as full professor. His current research interest is that using lead halide perovskite materials construct the functional optoelectronic devices, especially photodetectors and sensing devices.

Corresponding author: Jing Chen, chenjing@seu.edu.cn; Wei Lei, lw@seu.edu.cn; Xiaobao Xu, xiaobaoxu@seu.edu.cn

DOI: 10.1088/1674-4926/24100024CSTR: 32376.14.1674-4926.24100024

Abstract: Halide perovskites have attracted great interest as active layers in optoelectronic devices. Among perovskites with diverse compositions, α-FAPbI₃ is of utmost importance with great optoelectronic properties and a decent bandgap of 1.48 eV. However, the α-phase suffers an irreversible transition to the photo-inactive δ-phase, whereas the δ-phase is usually regarded as useless phase with poor optoelectronic properties. Therefore, it is commonly accepted that the thermodynamic stable δ-FAPbI₃ greatly limits the application of FAPbI₃. Every coin has two sides, although the δ-phase is difficult to apply as photoelectrical active layers, it is possible to combine δ-FAPbI₃ with α-FAPbI₃ to realize functional applications. Firstly, this review analyzes the cause of the contrasting properties between α- and δ-FAPbI₃, where the stronger electron−phonon coupling in 1D hexagonal δ-FAPbI₃ restricts its internal carrier and phonon transport. Secondly, the factors affecting the phase transitions and strategies to control phase transition between α- and δ-FAPbI₃ are presented. Finally, some functional applications of δ-FAPbI₃ in combination with α-FAPbI₃ are given according to previous reports. By and large, we hope to introduce δ-FAPbI₃ from another perspective and give some insights into its unique properties, hopefully providing new strategies for the subsequent advances to FAPbI₃.

Key words: halide perovskites, δ-FAPbI₃, α-FAPbI₃, electron−phonon coupling, phase transition

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Fig. 2. (Color online) (a) XRD patterns with different periodic alignments for α- and δ-FAPbI₃ single crystals and powder. (b) Different Raman shift for α- and δ-FAPbI₃. (a) and (b) Reprinted with permission from Ref. [44], Copyright 2023, American Chemical Society. (c) Temperature-dependent steady-state PL spectrum of α-FAPbI₃. (d) The extracted FWHM from steady-state PL spectrum of α-FAPbI₃, and the well fitted red line indicates contributions from inhomogeneous broadening and Fröhlich coupling. (c) and (d) Reprinted with permission from Ref. [38], Copyright 2016, published under the terms of the Creative Commons CC BY license.

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Fig. 3. (Color online) (a) Different structures of photoactive α-FAPbI₃ and photo-inactive δ-FAPbI₃. (b) Phonon density of states for the cubic, tetragonal, and hexagonal structures of FAPbI₃, where the blue and red peaks represent the vibrations of the PbI₃ octahedrons and FA⁺ cations, respectively. (a) and (b) Reprinted with permission from Ref. [33], Copyright 2022, American Chemical Society. (c) Schematic diagram of energy bands for STEs. Reprinted with permission from Ref. [24], Copyright 2020, Springer Nature. (d) PL spectra of α- and δ-FAPbI₃. Reprinted with permission from Ref. [44], Copyright 2023, American Chemical Society.

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Fig. 4. (Color online) (a)−(c) Real part of the permittivity of FAPbI₃ measured at 100 kHz during temperature cycles at different conditions. Reprinted with permission from Ref. [46], Copyright 2019, American Chemical Society. (d) Thermal diffusivity test of α- and δ-FAPbI₃. Reprinted with permission from Ref. [44], Copyright 2023, American Chemical Society.

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Fig. 5. (Color online) (a) Schematic diagram of Gibbs free energy for α- and δ-FAPbI₃. Reprinted with permission from Ref. [58], Copyright 2024, Elsevier. (b) The kinetic diagram with oriented and isotropic FA⁺ for cubic α-FAPbI₃ and hexagonal δ-FAPbI₃. Reprinted with permission from Ref. [59], Copyright 2016, published under the terms of the Creative Commons CC BY−NC license. (c) Phase stability comparison of α-FAPbI₃ films with/without internal strain. Reprinted with permission from Ref. [60], Copyright 2020, Springer Nature. (d) Phase transition diagram of α-FAPbI₃ during compression and decompression. Reprinted with permission from Ref. [22], Copyright 2018, American Chemical Society.

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Fig. 6. (Color online) (a) Schematic diagram of phase transition between α- and δ-FAPbI₃. Reprinted with permission from Ref. [58], Copyright 2024, published under the terms of the Creative Commons CC BY−NC−ND license. (b) Schematic diagram of the micro-area δ-to-α phase transition using direct-laser-writing. (c) Relationship between laser power and irradiation time of direct-laser-writing to realize δ-to-α phase transition. (d) Hybrid α-/δ-FAPbI₃ under visible light and UV light constructed by direct-laser-writing, and the relationship between linewidth of the phase transition region and laser power. (b)−(d) Reprinted with permission from Ref. [44], Copyright 2023, American Chemical Society.

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Fig. 7. (Color online) (a) Above-gap oscillations in the absorption spectra of FAPbI₃ films at different temperatures. The inset illustrates two mechanisms that may result in the oscillations: quantum confinement in deep wells and periodicity of the superlattice confining potential. Reprinted with permission from Ref. [67], Copyright 2020, Springer Nature. (b) Schematic diagram of α-FAPbI₃ single-crystal photothermal detector array, which denotes as device-α(SC) array, and the crosstalk of the nearest-neighbor and next-nearest-neighbor detection units in the device-α(SC) array. (c) Schematic diagram of hybrid α/δ-FAPbI₃ single-crystal photothermal detector array by direct-laser-writing, which denotes as device-α array, and the crosstalk of the nearest-neighbor and next-nearest-neighbor detection units in the device-α array. (d) Terahertz photothermal proof-of-concept imaging of the device-α(SC) array. (e) Terahertz photothermal proof-of-concept imaging of the device-α array. (b)−(e) Reprinted with permission from Ref. [44], Copyright 2023, American Chemical Society.

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Fig. 8. (Color online) (a) SEM images of micro-grating on α-FAPbI₃ film constructed by direct-laser-writing. (b) Schematic diagram of polarization photodetector with micro-grating. (c) Polarization performance of the α-FAPbI₃ photodetector with micro-grating, including angle-dependent photocurrent and linear sensitivity. (a)−(c) Reprinted with permission from Ref. [82], Copyright 2022, John Wiley and Sons.

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Fig. 9. (Color online) (a) Schematic diagram of the fabrication process of the α/δ-FAPbI₃ phase junction. (b) HRTEM of the α/δ-FAPbI₃ phase junction. (c) Schematic diagrams of the energy levels of pure α-FAPbI₃, pure δ-FAPbI₃, and the α/δ-FAPbI₃ phase junction. (d) Schematic diagram of the fabrication process of the bilayered δ-FAPbI₃/perovskite films. (e) Current density−voltage curves for devices based on pristine perovskite films and bilayered δ-FAPbI₃/perovskite films. (f) Statistics of PCEs and J_sc for devices based on pristine perovskite films and bilayered δ-FAPbI₃/perovskite films. (g) Evolution of PCEs for devices based on pristine perovskite films and bilayered δ-FAPbI₃/perovskite films under 40% ± 5% relative humidity (RH) at room temperature. (a)−(c) Reprinted with permission from Ref. [87], Copyright 2017, published under the terms of the Creative Commons CC BY−NC license. (d)−(g) Reprinted with permission from Ref. [88], Copyright 2022, John Wiley and Sons.

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Fig. 10. (Color online) (a) Schematic diagram of the fabrication process of δ-FAPbI₃ crystals, and the fabrication process of α-FAPbI₃ thin films using δ-FAPbI₃ crystals. (b) SEM image of the synthesized δ-FAPbI₃ crystal. (c) Current density-voltage curves for devices based on intermediate δ-FAPbI₃ single crystals (target) and powder sample (control). (d) Evolution of PCEs for target and control devices under continuous 1 sun illumination. (a)−(d) Reprinted with permission from Ref. [89], Copyright 2023, John Wiley and Sons.

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Table 1. The comparison of α-FAPbI₃ and δ-FAPbI₃.

Parameters	α-FAPbI₃	δ-FAPbI₃
Structure	Cubic structure (Pm$ \bar{3} $m) with corner-sharing octahedrons	Hexagonal structure (P6₃mc) with face-sharing octahedrons
Stability	Sensitive to humidity and oxygen
Temperature dependence	Thermodynamic instable at RT spontaneous transition to the δ-phase	Thermodynamically stable at RT transition to the α-phase via heating (about 150 °C )
Pressure influence	In compression process, α-FAPbI₃ undergoes Pm$ \bar{3} $m → P4/mbm → Im$ \bar{3} $ → partially amorphous from ambient pressure to 6.59 GPa, δ-FAPbI₃ converts to the orthorhombic Cmc2₁ structure between 1.26 and 1.73 GPa (the phase transition can also be recovered during the decompression process)
Mechanism of phase transition	The lower Gibbs free energy in δ-FAPbI₃ results in the inevitable α-to-δ phase transition at RT
Kinetics of transition	The driving force of the phase transition can be attributed to the temperature and internal/external pressure in the FAPbI₃ unit cells
Optoelectronic properties	Excellent	Poor
Applications	Acting as active layer materials	Assisting the photoactive α-FAPbI₃ layer for functional applications

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Received: 25 November 2024 Revised: 29 December 2024 Online: Accepted Manuscript: 04 January 2025Uncorrected proof: 18 February 2025

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Junyu Li, Songwei Zhang, Mohd Nazim Mohtar, Nattha Jindapetch, Istvan Csarnovics, Mehmet Ertugrul, Zhiwei Zhao, Jing Chen, Wei Lei, Xiaobao Xu. Advances in multi-phase FAPbI3 perovskite: another perspective on photo-inactive δ-phase[J]. Journal of Semiconductors, 2025, In Press. doi: 10.1088/1674-4926/24100024 ****J Y Li, S W Zhang, M N Mohtar, N Jindapetch, I Csarnovics, M Ertugrul, Z W Zhao, J Chen, W Lei, and X B Xu, Advances in multi-phase FAPbI3 perovskite: another perspective on photo-inactive δ-phase[J]. J. Semicond., 2025, 46(5), 051804 doi: 10.1088/1674-4926/24100024

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Junyu Li, Songwei Zhang, Mohd Nazim Mohtar, Nattha Jindapetch, Istvan Csarnovics, Mehmet Ertugrul, Zhiwei Zhao, Jing Chen, Wei Lei, Xiaobao Xu. Advances in multi-phase FAPbI₃ perovskite: another perspective on photo-inactive δ-phase[J]. Journal of Semiconductors, 2025, In Press. doi: 10.1088/1674-4926/24100024 ****

J Y Li, S W Zhang, M N Mohtar, N Jindapetch, I Csarnovics, M Ertugrul, Z W Zhao, J Chen, W Lei, and X B Xu, Advances in multi-phase FAPbI₃ perovskite: another perspective on photo-inactive δ-phase[J]. J. Semicond., 2025, 46(5), 051804 doi: 10.1088/1674-4926/24100024

Citation:

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Advances in multi-phase FAPbI₃ perovskite: another perspective on photo-inactive δ-phase

DOI: 10.1088/1674-4926/24100024

CSTR: 32376.14.1674-4926.24100024

1.
Joint International Research Laboratory of Information Display and Visualization, School of Electronic Science and Engineering, Southeast University, Nanjing 211189, China
2.
MyAgeingS1, University Putra Malaysia, Serdang, Selangor 43400, Malaysia
3.
Department of Electrical and Biomedical Engineering, Faculty of Engineering, Prince of Songkla University, Hat Yai, Songkhla 90110, Thailand
4.
Faculty of Science and Technology, University of Debrecen, Debrecen 4026, Hungary
5.
Department of Metallurgy and Material Science Engineering Composite Materials, Engineering Faculty, Karadeniz Technical University, Trabzon 61080, Turkey

More Information

Junyu Li received his Ph.D degree from Nanjing University of Science and Technology. He is currently a postdoctoral fellow in Joint International Research Laboratory of Information Display and Visualization, school of Electronic Science and Engineering, Southeast University. His current research interests focus on functional optoelectronic devices, especially terahertz sensing based on perovskite single crystals
Songwei Zhang is currently a master's student in Joint International Research Laboratory of Information Display and Visualization, school of Electronic Science and Engineering, Southeast University. He received his Bachelor’s degree in Electronic Science and Technology from Southeast University in 2023. His current research interests focus on perovskite X-ray detectors
Wei Lei received his Ph.D degree from Southeast University, China in 1994. After completing his doctoral studies, he worked in the department of Electronic Science and Engineering as assistant professor, associate professor, and professor. He is mainly involved in the field of the light emitting source, display, photo detection, and X-ray/ray imaging. A few novel materials, such as quantum dots, nano crystals, and perovskite single crystal, are used to improve the performance of light emitting device and photodetectors. In recent 5 years, more than 150 scientific journal papers have been published in these fields, and about 20 patents have been granted
Xiaobao Xu received his B.S. in Chemical Engineering and Technology and Ph.D in Optical Engineering from Huazhong University of Science and Technology in 2011 and 2016, respectively. He also studied in Prof. Yang Yang’s group (University of California, Los Angeles) as visiting student from 2014 to 2015 and worked in Prof. Alex Jen’s group (University of Washington, Seattle) as research associate from 2016−2018. Now, he works at Southeast University as full professor. His current research interest is that using lead halide perovskite materials construct the functional optoelectronic devices, especially photodetectors and sensing devices
Corresponding author: chenjing@seu.edu.cn; lw@seu.edu.cn; xiaobaoxu@seu.edu.cn
Received Date: 2024-11-25
Revised Date: 2024-12-29

Available Online: 2025-01-04

Abstract

Abstract

Halide perovskites have attracted great interest as active layers in optoelectronic devices. Among perovskites with diverse compositions, α-FAPbI₃ is of utmost importance with great optoelectronic properties and a decent bandgap of 1.48 eV. However, the α-phase suffers an irreversible transition to the photo-inactive δ-phase, whereas the δ-phase is usually regarded as useless phase with poor optoelectronic properties. Therefore, it is commonly accepted that the thermodynamic stable δ-FAPbI₃ greatly limits the application of FAPbI₃. Every coin has two sides, although the δ-phase is difficult to apply as photoelectrical active layers, it is possible to combine δ-FAPbI₃ with α-FAPbI₃ to realize functional applications. Firstly, this review analyzes the cause of the contrasting properties between α- and δ-FAPbI₃, where the stronger electron−phonon coupling in 1D hexagonal δ-FAPbI₃ restricts its internal carrier and phonon transport. Secondly, the factors affecting the phase transitions and strategies to control phase transition between α- and δ-FAPbI₃ are presented. Finally, some functional applications of δ-FAPbI₃ in combination with α-FAPbI₃ are given according to previous reports. By and large, we hope to introduce δ-FAPbI₃ from another perspective and give some insights into its unique properties, hopefully providing new strategies for the subsequent advances to FAPbI₃.
- halide perovskites,
- δ-FAPbI₃,
- α-FAPbI₃,
- electron−phonon coupling,
- phase transition

^§Junyu Li and Songwei Zhang contributed equally to this work and should be considered as co-first authors.

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