| 1. |
- Cai, Weidong, et al.
(författare)
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Multicolor light emission and multifunctional applications in double perovskite-Cs 2 NaInCl 6 by Cu + /Sb 3+co-doping
- 2024
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Ingår i: Chemical Engineering Journal. - : ELSEVIER SCIENCE SA. - 1385-8947 .- 1873-3212. ; 489
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Tidskriftsartikel (refereegranskat)abstract
- Halide double perovskites managed by metal doping approach can exhibit dual emission colors, which have been considered as promising multicolor luminescent materials. However, an independent and stable emission at yellow region is missing owing to limited doping candidates, hindering the further commercialization of multicolor luminescence applications in double perovskites. In this work, we successfully obtain stable multicolor emission with PLQE (photoluminescence quantum yield) as high as 78% through developing the CuI doping strategy in Sb-Cs2NaInCl6. By introducing a high CuI feed ratio in airtight autoclave to compete the oxidization effect, the oxidization of CuI into CuII (detrimental factor for high PLQE due to serious quenching effect) is largely suppressed. With changing the CuI feed ratio, at least four distinct emission colors ranging from blue, purple, pink to yellow can be realized via changing the excitation wavelength. Depending on tunable multicolor emission, we further demonstrate the promise of our co-doped double perovskites in anti-counterfeiting technology and multicolor lighting devices. Our results open the way for enriching the optical applications of double perovskites based on multicolor emission.
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| 2. |
- Ji, Fuxiang, et al.
(författare)
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Amine Gas-Induced Reversible Optical Bleaching of Bismuth-Based Lead-Free Perovskite Thin Films
- 2024
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Ingår i: Advanced Science. - : Wiley-VCH Verlagsgesellschaft. - 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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| 3. |
- 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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| 4. |
- Ji, Fuxiang, 1991-
(författare)
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Bandgap Engineering of Lead-Free Halide Double Perovskites
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lead-free halide double perovskites (HDPs, A2BIBIIIX6) with attractive optical and electronic features are regarded as one of the most promising alternatives to overcome the toxicity and stability issues of lead halide perovskites. They provide a wide range of possible combinations and rich substitutional chemistry with interesting properties for various optoelectronic devices. However, the performance of state-of-the-art lead-free HDPs is not yet comparable to that of lead halide perovskites, especially in the photovoltaic field. One of the main reasons for this is that HDPs usually have large and/or indirect bandgaps, which limit their optical and optoelectronic properties in the visible and infrared region. In this thesis, we attempt to modify the bandgap and optical properties of HDPs using metal doping/alloying and crystallization control, as well as provide detailed understanding of the alloying at the atomic level. We also observe significant changes of the bandgap of HDPs at different temperatures (i.e., thermochromism) and uncover the reasons behind it. We first adopt the metal doping/alloying strategy to alter the absorption properties of benchmark HDPs Cs2AgBiBr6. By introducing Cu as the dopant in Cs2AgBiBr6, we significantly broaden the absorption edge from around 610 nm to around 860 nm. Systematic characterizations indicate that Cu doping introduces defect states (sub-bandgap states) in the bandgap, without changing the bandgap of Cs2AgBiBr6. Interestingly, these sub-bandgaps can generate considerable amount of band carriers upon optical excitation, making these double perovskites promising for near-infrared light detection. In parallel with the material modification using the metal doping/alloying strategy, the fundamental understanding of these doped/alloyed double perovskite is also of critical importance. In the second paper, we reveal the atomic-level structure of alloyed double perovskites by presenting a series of double perovskite alloys with the chemical formula Cs2AgIn1-xFexCl6 (x = 0-1) showing tunable bandgaps in the range of 2.8-1.6 eV. Our results show that Fe3+ substitutes In3+ in the lattice with the formation of [FeCl6]3−·[AgCl6]5− domains, which grow larger gradually as the Fe3+ concentration increases. It is noted that these domains could be further connected to form microscopically segregated Fe3+-rich phases in the double perovskite alloys. To narrow the bandgap of Cs2AgBiBr6, we also develop a crystallization control approach, where high temperature is employed to assist the single crystal growth. By simply increasing the crystal growth temperature from 60 oC to 150 oC, the bandgap of Cs2AgBiBr6 crystals can be reduced from 1.98 eV to 1.72 eV, which is the lowest reported bandgap for Cs2AgBiBr6 at ambient conditions. The underlying reason is hypothesized to be related to the increased level of Ag–Bi disorder in the crystal structure. Lastly, we observe an interesting reversible thermochromic behavior in HDPs Cs2NaFeCl6. Specifically, the optical bandgap of Cs2NaFeCl6 is reduced from 2.06 eV to 1.86 eV when the temperature increases from RT to 150 oC and turns back to its original value after cooling. Meanwhile, we observe lattice expansion during the heating/ cooling process without phase transition. Our first-principles calculation indicates that the underlying mechanism for the thermochromic phenomenon in Cs2NaFeCl6 is mainly related to the electron-phonon coupling. Although the development of HDPs is in its early stages, we believe that HDPs with impressive optical and electronic properties and rich substitutional chemistry have a bright future in optoelectronic and multifunctional applications. Our findings shed new light to the absorption and bandgap modulation of HDPs and provide new insights into the atomic-level structures of DPAs, which can help to develop efficient optoelectronic devices.
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| 5. |
- 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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| 6. |
- Ji, Fuxiang, et al.
(författare)
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Lead-Free Halide Double Perovskite Cs2AgBiBr6 with Decreased Band Gap
- 2020
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Ingår i: Angewandte Chemie International Edition. - : Wiley-VCH Verlag. - 1433-7851 .- 1521-3773. ; 59:35, s. 15191-15194
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Tidskriftsartikel (refereegranskat)abstract
- Environmentally friendly halide double perovskites with improved stability are regarded as a promising alternative to lead halide perovskites. The benchmark double perovskite, Cs2AgBiBr6, shows attractive optical and electronic features, making it promising for high-efficiency optoelectronic devices. However, the large band gap limits its further applications, especially for photovoltaics. Herein, we develop a novel crystal-engineering strategy to significantly decrease the band gap by approximately 0.26 eV, reaching the smallest reported band gap of 1.72 eV for Cs2AgBiBr6 under ambient conditions. The band-gap narrowing is confirmed by both absorption and photoluminescence measurements. Our first-principles calculations indicate that enhanced Ag/Bi disorder has a large impact on the band structure and decreases the band gap, providing a possible explanation of the observed band-gap narrowing effect. This work provides new insights for achieving lead-free double perovskites with suitable band gaps for optoelectronic applications.
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| 7. |
- Ji, Fuxiang, et al.
(författare)
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Near-Infrared Light-Responsive Cu-Doped Cs2AgBiBr6
- 2020
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Ingår i: Advanced Functional Materials. - : WILEY-V C H VERLAG GMBH. - 1616-301X .- 1616-3028. ; 30:51
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Tidskriftsartikel (refereegranskat)abstract
- Lead-free halide double perovskites (A(2)B(I)B(III)X(6)) with attractive optical and electronic features are considered to be a promising candidate to overcome the toxicity and stability issues of lead halide perovskites (APbX(3)). However, their poor absorption profiles limit device performance. Here the absorption band edge of Cs(2)AgBiBr(6)double perovskite to the near-infrared range is significantly broadened by developing doped double perovskites, Cs-2(Ag:Cu)BiBr6. The partial replacement of Ag ions by Cu ions in the crystal lattice is confirmed by the X-ray photoelectron spectroscopy (XPS) and solid-state nuclear magnetic resonance (ssNMR) measurements. Cu doping barely affects the bandgap of Cs2AgBiBr6; instead it introduces subbandgap states with strong absorption to the near-infrared range. More interestingly, the near-infrared absorption can generate band carriers upon excitation, as indicated by the photoconductivity measurement. This work sheds new light on the absorption modulation of halide double perovskites for future efficient optoelectronic devices.
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| 8. |
- 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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| 9. |
- Ji, Fuxiang, 1991-, et al.
(författare)
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Remarkable Thermochromism in the Double Perovskite Cs2NaFeCl6
- 2024
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Ingår i: Advanced Optical Materials. - : John Wiley & Sons. - 2162-7568 .- 2195-1071. ; 12:8
-
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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| 10. |
- Ji, Fuxiang, et al.
(författare)
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The atomic-level structure of bandgap engineered double perovskite alloys Cs2AgIn1-xFexCl6
- 2021
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 12:5, s. 1730-1735
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Tidskriftsartikel (refereegranskat)abstract
- Although lead-free halide double perovskites are considered as promising alternatives to lead halide perovskites for optoelectronic applications, state-of-the-art double perovskites are limited by their large bandgap. The doping/alloying strategy, key to bandgap engineering in traditional semiconductors, has also been employed to tune the bandgap of halide double perovskites. However, this strategy has yet to generate new double perovskites with suitable bandgaps for practical applications, partially due to the lack of fundamental understanding of how the doping/alloying affects the atomic-level structure. Here, we take the benchmark double perovskite Cs2AgInCl6 as an example to reveal the atomic-level structure of double perovskite alloys (DPAs) Cs2AgIn1-xFexCl6 (x = 0-1) by employing solid-state nuclear magnetic resonance (ssNMR). The presence of paramagnetic alloying ions (e.g. Fe3+ in this case) in double perovskites makes it possible to investigate the nuclear relaxation times, providing a straightforward approach to understand the distribution of paramagnetic alloying ions. Our results indicate that paramagnetic Fe3+ replaces diamagnetic In3+ in the Cs2AgInCl6 lattice with the formation of [FeCl6](3-)center dot[AgCl6](5-) domains, which show different sizes and distribution modes in different alloying ratios. This work provides new insights into the atomic-level structure of bandgap engineered DPAs, which is of critical significance in developing efficient optoelectronic/spintronic devices.
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