| 1. |
- Chen, Yujie, et al.
(författare)
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Unraveling dual phase transformations in a CrCoNi medium-entropy alloy
- 2021
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 215
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Tidskriftsartikel (refereegranskat)abstract
- The emergence of multi-principal element alloys (MPEAs) holds great promise for the development of high performance metallic materials. However, it remains unclear whether MPEAs can provide previously unknown deformation mechanisms to drastically enhance their mechanical performance. Here we report a new deformation mechanism of mechanically-induced dual phase transformations from the face-centered cubic (FCC) to hexagonal close- packed (HCP) phase and then back to the FCC phase with nanotwins in a CrCoNi medium-entropy alloy (MEA). During the two sequential steps of phase transformation, continued shear occurs in the same < 110 >(FCC) parallel to < 11 (2) over bar0 >(HCP) direction along different {111}(FCC) parallel to (0001)(HCP) planes, producing a total shear transformation strain up to 70%. The dual phase transformations stem from a unique capability of facile slip in between the close-packed {111}(FCC) parallel to (0001)(HCP) atomic layers in both FCC and HCP phases, leading to flexible stacking sequences of those close-packed layers with low stacking fault energies. Our work demonstrates that MPEAs can offer unconventional deformation mechanisms such as dual phase transformations in the CrCoNi MEA, thereby opening opportunities for enhancing the mechanical properties of advanced alloys.
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| 2. |
- Wen, Guanzhao, et al.
(författare)
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Energy level offsets determine the interplay between charge and energy transfer in all-small-molecule organic solar cells
- 2023
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Ingår i: Chemical Engineering Journal. - 1385-8947. ; 475
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Tidskriftsartikel (refereegranskat)abstract
- All-small-molecule organic solar cells (ASM OSCs) hold great promise in OSCs owing to their defined structures, simple purification, and good reproducibility, but are challenging for further improved efficiency. The energy level strategy has been broadly applied to obtain a better performance; however, a comprehensive understanding of the effects of energy level offset on photoexcitation dynamics in ASM OSCs is rarely studied. Herein, for Y-series molecules (Y6, Y10, Y5, and BTP-4F-12) based ASM OSCs, the effect of energy level offset on charge photogeneration was investigated using steady-state and time-resolved spectroscopies. We found that both energy and charge transfer could occur in blend films. A method to quantitatively analyze the contribution of charge and energy transfer processes was developed. For BTR-Cl:Y6 with the highest LUMO level offset, ∼ 23% of photogenerated excitons in donor dissociated via “energy transfer and the subsequent charge transfer” pathway, suggesting that the energy transfer in blend films should also be considered. And for the hole transfer, the excitons in Y-series molecules can only be effectively dissociated when the HOMO energy level offset is higher than 0.11 eV. Besides, a higher energy level offset would also suppress carrier recombination in ultrafast timescale. These results may shed light on the design of ASM OSCs.
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| 3. |
- Gao, Feng, et al.
(författare)
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Visible-light photocatalytic properties of weak magnetic BiFeO3 nanoparticles
- 2007
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Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 19:19, s. 2889-2892
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Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline BiFeO3 nanoparticles (size 80-120 nm) are prepared by a simple sol-gel technique. Such nanoparticles are very efficient for photocatalytic decomposition of organic contaminants under irradiation from ultraviolet to visible frequencies. The BiFeO3 nanoparticles also demonstrate weak ferromagnetism of about 0.06 mu(B)/Fe at room temperature, in good agreement with theoretical calculations.
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| 4. |
- Wen, Guanzhao, et al.
(författare)
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Excited-state properties of Y-series small molecule semiconductors
- 2021
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Ingår i: Dyes and Pigments. - : Elsevier BV. - 0143-7208. ; 192
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Tidskriftsartikel (refereegranskat)abstract
- The emergence of the Y series small molecule semiconductors, Y6 and its derivatives, have significantly improved the performance of polymer solar cells (PSCs). However, the excited-state properties of these Y-series small molecule semiconductors which are highly important for designing high-performance PSCs, need to be illustrated. In this work, the excited-state properties and electronic structures of the Y-series small molecules (Y5, Y6, Y10, N3, Y6-BO-4F, and Y6-BO-4Cl) have been systematically studied by using steady-state and time-resolved spectroscopies and quantum chemical calculations. It is shown that the influence of alkyl chains at the nitrogen atom of the pyrrole ring is weak for the electron affinities, ionization potentials, electron and hole reorganization energies and singlet exciton lifetime of Y molecules. Meanwhile, these parameters are found to be varied with the types of electron-deficient termini. Moreover, we find that Y10 and Y5 have the shortest singlet exciton lifetime in solution and the longest singlet exciton lifetime in film (~1100 ps), suggesting the engineering of electron-deficient termini can significantly influence the excited-state lifetime in solution and film. Our work could provide a guideline for designing Y-series acceptor materials for high-performance polymer solar cells.
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| 5. |
- Wen, Guanzhao, et al.
(författare)
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Ground- And excited-state characteristics in photovoltaic polymer N2200
- 2021
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 11:33, s. 20191-20199
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Tidskriftsartikel (refereegranskat)abstract
- As a classical polymer acceptor material, N2200 has received extensive attention and research in the field of polymer solar cells (PSCs). However, the intrinsic properties of ground- and excited-states in N2200, which are critical for the application of N2200 in PSCs, remain poorly understood. In this work, the ground- and excited-state properties of N2200 solution and film were studied by steady-state and time-resolved spectroscopies as well as time-dependent density functional theory (TD-DFT) calculations. The transition mechanism of absorption peaks of N2200 was evaluated through the natural transition orbitals (NTOs) and hole-electron population analysis by TD-DFT. Time-resolved photoluminescence (TRPL) study shows that the lifetimes of singlet excitons in N2200 chlorobenzene solution and film are ∼90 ps and ∼60 ps, respectively. Considering the absolute quantum yield of N2200 film, we deduce that the intrinsic lifetime of singlet exciton can be as long as ∼20 ns. By comparing the TRPL and transient absorption (TA) kinetics, we find that the decay of singlet excitons in N2200 solution is dominated by a fast non-radiative decay process, and the component induced by intersystem crossing is less than 5%. Besides that, the annihilation radius, annihilation rate and diffusion length of singlet excitons in N2200 film were evaluated as 3.6 nm, 2.5 × 10−9cm3s−1and 4.5 nm, respectively. Our work provides comprehensive information on the excited states of N2200, which is helpful for the application of N2200 in all-PSCs.
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| 6. |
- Zhang, Jibin, et al.
(författare)
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A Multifunctional "Halide-Equivalent" Anion Enabling Efficient CsPb(Br/I)(3) Nanocrystals Pure-Red Light-Emitting Diodes with External Quantum Efficiency Exceeding 23%
- 2023
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Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 35:8
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Tidskriftsartikel (refereegranskat)abstract
- Pure-red perovskite LEDs (PeLEDs) based on CsPb(Br/I)(3) nanocrystals (NCs) usually suffer from a compromise in emission efficiency and spectral stability on account of the surface halide vacancies-induced nonradiative recombination loss, halide phase segregation, and self-doping effect. Herein, a "halide-equivalent" anion of benzenesulfonate (BS-) is introduced into CsPb(Br/I)(3) NCs as multifunctional additive to simultaneously address the above challenging issues. Joint experiment-theory characterizations reveal that the BS- can not only passivate the uncoordinated Pb2+-related defects at the surface of NCs, but also increase the formation energy of halide vacancies. Moreover, because of the strong electron-withdrawing property of sulfonate group, electrons are expected to transfer from the CsPb(Br/I)(3) NC to BS- for reducing the self-doping effect and altering the n-type behavior of CsPb(Br/I)(3) NCs to near ambipolarity. Eventually, synergistic boost in device performance is achieved for pure-red PeLEDs with CIE coordinates of (0.70, 0.30) and a champion external quantum efficiency of 23.5%, which is one of the best value among the ever-reported red PeLEDs approaching to the Rec. 2020 red primary color. Moreover, the BS--modified PeLED exhibits negligible wavelength shift under different operating voltages. This strategy paves an efficient way for improving the efficiency and stability of pure-red PeLEDs.
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| 7. |
- Zhang, Jibin, et al.
(författare)
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Ligand-Induced Cation-p Interactions Enable High-Efficiency, Bright, and Spectrally Stable Rec. 2020 Pure-Red Perovskite Light-Emitting Diodes
- 2023
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Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095.
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Tidskriftsartikel (refereegranskat)abstract
- Achieving high-performance perovskite light-emitting diodes (PeLEDs) with pure-red electroluminescence for practical applications remains a critical challenge because of the problematic luminescence property and spectral instability of existing emitters. Herein, high-efficiency Rec. 2020 pure-red PeLEDs, simultaneously exhibiting exceptional brightness and spectral stability, based on CsPb(Br/I)(3) perovskite nanocrystals (NCs) capping with aromatic amino acid ligands featuring cation-pi interactions, are reported. It is proven that strong cation-pi interactions between the PbI6-octahedra of perovskite units and the electron-rich indole ring of tryptophan (TRP) molecules not only chemically polish the imperfect surface sites, but also markedly increase the binding affinity of the ligand molecules, leading to high photoluminescence quantum yields and greatly enhanced spectral stability of the CsPb(Br/I)(3) NCs. Moreover, the incorporation of small-size aromatic TRP ligands ensures superior charge-transport properties of the assembled emissive layers. The resultant devices emitting at around 635 nm demonstrate a champion external quantum efficiency of 22.8%, a max luminance of 12 910 cd m(-2), and outstanding spectral stability, representing one of the best-performing Rec. 2020 pure-red PeLEDs achieved so far.
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| 8. |
- Zhang, Wei, et al.
(författare)
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Effect of post-thermal annealing on the performance and charge photogeneration dynamics of PffBT4T-2OD/PC71BM solar cells
- 2019
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 11:3
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we studied influence of post thermal annealing on the performance and charge photogeneration processes of PffBT4T-2OD/PC 71 BM solar cells. As-prepared device exhibits a high-power conversion efficiency of 9.5%, much higher than that after thermal annealing. To understand this phenomenon, we studied charge photogeneration processes in these solar cells by means of time resolved spectroscopy. We associate the degradation of solar cell performance with the reduction of exciton dissociation efficiency and with increased bimolecular recombination of photogenerated charges as a result of annealing. We correlate the generation of localized PffBT4T-2OD polarons observed via spectro-electrochemical measurements with enhancement of the bimolecular charge recombination of annealed solar cells.
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