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| 2. |
- Zou, Kai, et al.
(författare)
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Fractal superconducting nanowire single-photon detectors working in dual bands and their applications in free-space and underwater hybrid LIDAR
- 2023
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Ingår i: Optics Letters. - : Optica Publishing Group. - 0146-9592 .- 1539-4794. ; 48:2, s. 415-418
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a fiber-coupled fractal superconducting nanowire single-photon detector (SNSPD) system with minimum polarization dependence of detection efficiency. Its system detection efficiency (SDE) was maximized at the wavelength of 1540 nm, which was measured to be 91 +/- 4%; furthermore, we observed the second local maximum of SDE at the wavelength of 520 nm, which was measured to be 61 +/- 2%. This dual-band feature of SDE was due to the enhancement of the optical absorptance by two longitudinal resonance modes of the micro-cavity. By using high SDE with minimum polarization dependence in these two bands, we implemented a hybrid LIDAR for imaging the remote objects in free space and under water.
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| 3. |
- Feng, Junyi, et al.
(författare)
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The Role of Energy Offsets on Charge Photogeneration Dynamics in Y-Series Molecules-Based Polymer Solar Cells
- 2023
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Ingår i: Solar RRL. - 2367-198X. ; 7:16
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Tidskriftsartikel (refereegranskat)abstract
- Recent research has revealed that low-energy offset polymer solar cells (PSCs) are capable of a power conversion efficiency of over 19%. However, it is unclear how energy offsets and the charge photogeneration process are correlated. Herein, the effect of energy offsets on charge photogeneration dynamics for Y-series molecules (Y5, Y6, Y10, and BTP-4F-12)-based PSCs with the variations of the lowest unoccupied molecular orbital energy offsets (ΔELUMO) of 0.11–0.42 eV and the highest occupied molecular orbital energy offsets (ΔEHOMO) of 0.08–0.23 eV utilizing steady-state and time-resolved spectroscopies is studied. The steady-state measurement shows that the probability of photoluminescence quenching via energy transfer for the donor exciton reduces with the increasing ΔELUMO. It is found that even in PM6:Y6 with the highest ΔELUMO, ≈18% of PM6 exciton dissociated via the path of “energy transfer first and then hole transfer,” manifesting the energy transfer also plays a vital role in the process of exciton dissociation. Furthermore, it is found that the PM6 exciton can efficiently dissociate under the ΔELUMO of 0.11 eV. After photoexcitation of the Y-series molecule acceptors, the exciton dissociation efficiency enhances with the increase of ΔEHOMO. Besides, the higher energy offsets, the lower charge recombination rate in the ultrafast timescale has been found from the transient absorption measurement. These findings reveal that energy offsets are important for charge photogeneration and recombination in an ultrafast timescale for Y-series molecule-based PSCs, which may shed light on the design of high-performance PSCs.
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| 4. |
- Geng, Huifang, et al.
(författare)
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Controlled synthesis of highly stable lead-free bismuth halide perovskite nanocrystals : tructures and photophysics
- 2023
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Ingår i: SCIENCE CHINA Materials. - : Springer Science and Business Media LLC. - 2095-8226 .- 2199-4501. ; 66:5, s. 2079-2089
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Tidskriftsartikel (refereegranskat)abstract
- Recently, cesium bismuth halide perovskites have emerged as potential substitutes to their counterparts, cesium lead halide perovskites, owing to their low toxicity. However, the photophysics of cesium-bismuth halides nanocrystals (NCs) have not yet been fully rationalized because their structures remain highly debated. The ultraviolet-visible (UV-vis) absorption along with other photophysical properties such as the nature and lifetime of the excited states vary considerably across the previous reports. Here, we successfully synthesize pure Cs3BiBr6 and Cs3Bi2Br9 NCs via a modified hot-injection method, where the structure can be easily controlled by tuning the reaction temperature. The UV-vis absorption spectrum of the pure Cs3Bi2Br9 NCs features two characteristic peaks originating from the absorption of the first exciton and second exciton, respectively, which ultimately clarifies the debate in the previous reports. Using femtosecond transient absorption spectroscopy, we systematically investigate the excited state dynamics of the Cs3Bi2Br9 NCs and reveal that the photoexcited carriers undergo a self-trapping process within 3 ps after excitation. More intriguingly, the Cs3Bi2Br9 NCs prepared by this method show much better photostability than those prepared by the ligand-assisted reprecipitation process. Photodetectors based on these Cs3Bi2Br9 NCs show a sensitive light response, demonstrating the definite potential for breakthrough optoelectronic applications. [Figure not available: see fulltext.].
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| 5. |
- Hu, Guojie, et al.
(författare)
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Water and heat coupling processes and its simulation in frozen soils : Current status and future research directions
- 2023
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Ingår i: Catena. - : Elsevier BV. - 0341-8162. ; 222
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Forskningsöversikt (refereegranskat)abstract
- To date, most studies on coupled-water-and-heat processes in frozen soils haves focused on the mechanism of changes in frozen soil and the contribution of climate change, hydrological processes, and ecosystems in cold regions. Several studies have demonstrated considerable improvements in the accuracy of simulating water and heat transfer processes in cold regions. However, substantial differences remain among the different models and parameterizations because of the lack of observations and in-depth understanding of the water and heat transfer processes. Hence, it is necessary to summarize recent advances in the simulation of water-and-heat-coupling processes and challenges for further research. Therefore, we present a theory-focused summary of progress in this field considering the aspects of water flow and coupled-water-and-heat transfer. The simulation progress is discussed in terms of physical process models; one type of model only considers the heat conduction transfer processes without water flow, and the other considers coupled-water-and-heat transfer processes. Aspects of model deficiencies related to non-conductive heat transfer and soil water transfer processes in the frozen soil are also summarized. Moreover, the major parameterizations are reviewed, including phase changes, freeze–thaw fronts, thermal conductivity, hydraulic conductivity, snow processes, surface parameterization schemes, ground ice, and lower boundary conditions. While models and parameterizations can suitably capture local-scale water and heat transfer processes in frozen soil, their applications are spatiotemporally constrained, requiring further improvement. We provide a theoretical basis for further studying water and heat transfer processes in frozen soil and suggest that future research should enhance the accuracy of frozen soil parameterization and improve the understanding of the coupling of water and heat transfer processes based on improved observation techniques and high-resolution data.
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| 6. |
- Liu, Wei, et al.
(författare)
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The Synthesis of a Multiple D-A Conjugated Macrocycle and Its Application in Organic Photovoltaic
- 2023
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Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773.
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Tidskriftsartikel (refereegranskat)abstract
- As a novel class of materials, D-A conjugated macrocycles hold significant promise for chemical science. However, their potential in photovoltaic remains largely untapped due to the complexity of introducing multiple donor and acceptor moieties into the design and synthesis of cyclic pi-conjugated molecules. Here, we report a multiple D-A ring-like conjugated molecule (RCM) via the coupling of dimer molecule DBTP-C3 as a template and thiophenes in high yields. RCM exhibits a narrow optical gap (1.33 eV) and excellent thermal stability, and shows a remarkable photoluminescence yield (phi PL) of 11.1 % in solution, much higher than non-cyclic analogues. Organic solar cell (OSC) constructed with RCM as electron acceptor shows efficient charge separation at donor-acceptor band offsets and achieves a power conversion efficiency (PCE) of 14.2 %-approximately fourfold higher than macrocycle-based OSCs reported so far. This is partly due to low non-radiative voltage loss down to 0.20 eV and a high electroluminescence yield (phi EL) of 4x10-4. Our findings emphasize the potential of D-A cyclic conjugated molecules in advancing organic photovoltaic technology. A multiple D-A ring-like conjugated molecule, RCM was synthesized via a template-directed process. RCM inherits the superior photovoltaic properties characteristic of D-A linear molecules, including a narrow optical gap and effective charge transfer. Importantly, RCM demonstrates reduced non-radiative losses, attributable to its minimized vibration.+image
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| 7. |
- Luo, Yifei, et al.
(författare)
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Technology Roadmap for Flexible Sensors
- 2023
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Ingår i: ACS Nano. - : American Chemical Society. - 1936-0851 .- 1936-086X. ; 17:6, s. 5211-5295
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Forskningsöversikt (refereegranskat)abstract
- Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.
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| 8. |
- 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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| 9. |
- Xu, Jiawei, et al.
(författare)
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Optoelectronic memristor model for optical synaptic circuit of spiking neural networks
- 2023
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Ingår i: 21st IEEE Interregional NEWCAS Conference, NEWCAS 2023. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- Optoelectronic memristors are suitable candidates for hardware implementation of optical synapses in spiking neural networks (SNNs), thanks to their electrical and optical characteristics. To study the feasibility of memristor-based optical synapses in SNNs, a behavior model for optoelectronic memristors is proposed in this paper, including electrical programming modeling and photocurrent read modeling. Based on the model, the behavior of a molecular ferroelectric (MF)/semiconductor interfacial memristor is simulated. This paper also proposes an optical synaptic circuit for trace-based spike-timing-dependent plasticity (STDP) learning rule. The electrical characteristics of the memristor are explored and exploited to emulate the trace in the pairwise nearest-neighbor STDP, while the optical characteristics are utilized for non-destructive readout and weight calculation. Synaptic-level simulation results show a 99.96% correlation coefficient (CC) and a 1.91% relative root mean square error (RRMSE) in the weight approximate computation. Extending the simulation to the network level, the optoelectronic memristor-based unsupervised STDP learning system can achieve a 92.07± 0.64% accuracy on the MNIST benchmark.
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| 10. |
- Xu, T., et al.
(författare)
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Hydrate salt/fumed silica shape-stabilized composite phase change material with adjustable phase change temperature for radiant floor heating system
- 2023
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Ingår i: Journal of Building Engineering. - : Elsevier. - 2352-7102. ; 71
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Tidskriftsartikel (refereegranskat)abstract
- Radiant floor heating system combined with hydrate salt phase change materials (PCMs) can obtain energy savings along with improving thermal comfort. However, the inappropriate phase change temperature and the leakage of PCM limit its further applications. Here, sodium acetate trihydrate (SAT)-potassium chloride (KCl)-urea composite phase change material (CPCM) was composited with fumed silica (SiO2) to prepare shape-stabilized CPCM (SSCPCM) with adjustable phase change temperature for use in floor radiant heating. The effects of the mass fraction of SiO2 on phase change properties, and shape-stabilized ability of SSCPCM were emphatically studied. Besides, the morphology, porous structure analysis and chemical compatibility and related thermal properties of SSCPCM were discussed detailedly. The results manifested that SiO2 could not only regulate the melting temperature of SAT-KCl-urea CPCM, but also stabilize CPCM into its porous structure with large surface area and high porosity. Meanwhile, SSCPCM with 30 wt% SiO2 exhibited a good shape stability, and melted at 40.85 °C with high latent heat of 132.6 J/g, low supercooling degree of 0.29 °C as well as good thermal stability and thermal reliability. The result comparison of two test rooms confirmed that phase change floor radiant heating system can effectively increase the duration of indoor thermal comfort. All good thermal properties of SSCPCM make it prospective potential in radiant floor heating system for building energy efficiency. © 2023 Elsevier Ltd
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