| 1. |
- Ji, Fuxiang, et al.
(författare)
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Amine Gas‐Induced Reversible Optical Bleaching of Bismuth‐Based Lead‐Free Perovskite Thin Films
- 2023
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Ingår i: Advanced Science. - : WILEY. - 2198-3844. ; 11:4
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Tidskriftsartikel (refereegranskat)abstract
- Reversible optical property changes in lead-free perovskites have recently received great interest due to their potential applications in smart windows, sensors, data encryption, and various on-demand devices. However, it is challenging to achieve remarkable color changes in their thin films. Here, methylamine gas (CH3NH2, MA0) induced switchable optical bleaching of bismuth (Bi)-based perovskite films is demonstrated for the first time. By exposure to an MA0 atmosphere, the color of Cs2AgBiBr6 (CABB) films changes from yellow to transparent, and the color of Cs3Bi2I9 (CBI) films changes from dark red to transparent. More interestingly, the underlying reason is found to be the interactions between MA0 and Bi3+ with the formation of an amorphous liquefied transparent intermediate phase, which is different from that of lead-based perovskite systems. Moreover, the generality of this approach is demonstrated with other amine gases, including ethylamine (C2H5NH2, EA0) and butylamine (CH3(CH2)3NH2, BA0), and another compound, Cs3Sb2I9, by observing a similar reversible optical bleaching phenomenon. The potential for the application of CABB and CBI films in switchable smart windows is investigated. This study provides valuable insights into the interactions between amine gases and lead-free perovskites, opening up new possibilities for high-efficiency optoelectronic and stimuli-responsive applications of these emerging Bi-based materials.
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| 2. |
- Ji, Fuxiang, 1991-, et al.
(författare)
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Challenges and Progress in Lead-Free Halide Double Perovskite Solar Cells
- 2023
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Ingår i: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; 7:6
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Tidskriftsartikel (refereegranskat)abstract
- Lead-free halide double perovskites (HDPs) with a chemical formula of A(2)B(+)B(3+)X(6) are booming as attractive alternatives to solve the toxicity issue of lead-based halide perovskites (APbX(3)). HDPs show excellent stability, a wide range of possible combinations, and attractive optoelectronic features. Although a number of novel HDPs have been studied, the power conversion efficiency of the state-of-the-art double perovskite solar cell is still far inferior to that of the dominant Pb-based ones. Understanding the fundamental challenges is essential for further increasing device efficiency. In this review, HDPs with attractive electronic and optical properties are focused on, and current challenges in material properties and device fabrication that limit high-efficiency photovoltaics are analyzed. Finally, the promising approaches and views to overcome these bottlenecks are highlighted.
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| 3. |
- Ji, Fuxiang, 1991-, et al.
(författare)
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Remarkable Thermochromism in the Double Perovskite Cs2NaFeCl6
- 2023
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Ingår i: Advanced Optical Materials. - : Wiley-Blackwell. - 2162-7568 .- 2195-1071.
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Tidskriftsartikel (refereegranskat)abstract
- Lead-free halide double perovskites (HDPs) have emerged as a new generation of thermochromic materials. However, further materials development and mechanistic understanding are required. Here, a highly stable HDP Cs2NaFeCl6 single crystal is synthesized, and its remarkable and fully reversible thermochromism with a wide color variation from light-yellow to black over a temperature range of 10 to 423 K is investigated. First-principles, density functional theory (DFT)-based calculations indicate that the thermochromism in Cs2NaFeCl6 is an effect of electron–phonon coupling. The temperature sensitivity of the bandgap in Cs2NaFeCl6 is up to 2.52 meVK−1 based on the Varshni equation, which is significantly higher than that of lead halide perovskites and many conventional group-IV, III–V semiconductors. Meanwhile, this material shows excellent environmental, thermal, and thermochromic cycle stability. This work provides valuable insights into HDPs' thermochromism and sheds new light on developing efficient thermochromic materials.
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| 4. |
- Zhang, Bin, et al.
(författare)
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Lattice Dynamics and Electron-Phonon Coupling in Double Perovskite Cs2NaFeCl6
- 2023
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:4, s. 1908-1916
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Tidskriftsartikel (refereegranskat)abstract
- Phonon-phonon and electron/exciton-phonon coupling play a vitally important role in thermal, electronic, as well as optical properties of metal halide perovskites. In this work, we evaluate phonon anharmonicity and coupling between electronic and vibrational excitations in novel double perovskite Cs2NaFeCl6 single crystals. By employing comprehensive Raman measurements combined with first-principles theoretical calculations, we identify four Raman-active vibrational modes. Polarization properties of these modes imply Fm (3) over barm symmetry of the lattice, indicative for on average an ordered distribution of Fe and Na atoms in the lattice. We further show that temperature dependence of the Raman modes, such as changes in the phonon line width and their energies, suggests high phonon anharmonicity, typical for double perovskite materials. Resonant multiphonon Raman scattering reveals the presence of high-lying band states that mediate strong electron-phonon coupling and give rise to intense nA(1g) overtones up to the fifth order. Strong electron-phonon coupling in Cs2NaFeCl6 is also concluded based on the Urbach tail analysis of the absorption coefficient and the calculated Frohlich coupling constant. Our results, therefore, suggest significant impacts of phonon-phonon and electron-phonon interactions on electronic properties of Cs2NaFeCl6, important for potential applications of this novel material.
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| 5. |
- Zhang, Bin, et al.
(författare)
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Photoactivated Second Harmonic Generation in Centrosymmetric Double Perovskites
- 2023
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 10:9, s. 3350-3358
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Tidskriftsartikel (refereegranskat)abstract
- We report the firstobservation of second harmonic generation (SHG)from halide double perovskites single crystals, a promising classof materials for low-cost and versatile optoelectronic applications,owing to their enormous structural flexibility and environmental friendliness.We show that the SHG efficiency of these materials with centrosymmetriccrystalline structures critically depends on the measurement temperature.At high temperatures, it is determined by a surface contribution butincreases by up to 3 orders of magnitude at low temperatures (T < 137 K for Cs2NaFeCl6 and T < 250 K for Cs2AgBiBr6) underlight illumination within several minutes. We attribute this enhancementto the build-up of a light-induced electric field within the near-surfaceregion, which generates an additional contribution to the SHG process.This DC electric field is found to be predominantly oriented orthogonallyto the sample surface, as deduced from the six-fold rotational symmetryof the SHG azimuthal pattern. The electric field formation is explainedby photoinduced charge transfer from deep surface-related states totraps in the bulk region or vice versa, mainly driven by diffusion.Furthermore, the inscribed electric field can be maintained for hoursat low temperatures and can only be erased by raising the temperaturedue to carrier detrapping. Our findings, therefore, highlight theimportance of the surface states in double perovskites, which couldbe utilized for enhancing the nonlinear properties of these centrosymmetricmaterials.
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