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All-Dielectric Metasurface-Enabled Near-Infrared Switching Based on Ge2Sb2Te5 Phase-Change Material
摘要： A metasurface for use in multiscale applications in the near-infrared (NIR) range is proposed herein. A detailed study is carried out on a polarization-insensitive, single-layered, recon?gurable swastika-like metasurface for NIR switching. Using germanium antimony telluride (Ge2Sb2Te5) as a phase-change material, the metasurface works as a NIR switch in the wavelength range from 1.8 lm and 2.2 lm. The metasurface consists of a patterned Ge2Sb2Te5 thin ?lm on a glass substrate, making it an all-dielectric metastructure. A high switching contrast ratio, i.e., ratio of maximum to minimum transmission, of 150 was obtained. Light with different polarizations had no effect on the switching behavior of the metasurface, making it a potential candidate for the development of advanced, tunable, and integrated photonic devices.
关键词： optical switch,phase-change material,toroidal dipole resonances,Metasurface
更新于2025-09-23 15:19:57
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Origin of short- and medium-range order in supercooled liquid Ge <sub/>3</sub> Sb <sub/>2</sub> Te <sub/>6</sub> using <i>ab initio</i> molecular dynamics simulations
摘要： Phase-change materials such as Ge-Sb-Te compounds have attracted much attention due to the potential value for electrical data storage. In contrast to the amorphous and crystalline phases, supercooled liquid is far from to be deeply understood despite of the inevitable role in both amorphization and crystallization process. To this end, we have studied the dynamics property and structural characteristic of liquid and supercooled liquid Ge3Sb2Te6 during the fast cooling process. As the temperature decreases, chemical bonds become more homogeneous, but coordination numbers of Ge, Sb and Te atoms change very little. Meanwhile, the structural order of short-range configuration is obvious enhanced. Further studies suggest that Ge-centered, Sb-centered and Te-centered configurations change to the more ordered defective octahedrons mainly by adjusting the bond-angle relation and bond length, rather than just changing the coordination environment. It is the more ordered octahedrons that promote the formation of medium-range order. Our findings provide a deep insight on the origin of local structural order in supercooled liquid Ge3Sb2Te6, which are of great importance for the comprehensive understanding of amorphization and crystallization processes.
关键词： molecular dynamics,phase-change material,supercooled liquid,short-range order
更新于2025-09-23 15:19:57
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Solar gain mitigation in ventilated tiled roofs by using phase change materials
摘要： Several passive cooling design techniques are known for reducing solar heat gain through building envelope in summer season. These include the use of phase change materials (PCM), which has received an increased attention over the last years, and the strategy of increasing the above-sheathing ventilation (ASV) in ventilated roofs. However, few studies combine both technologies to maximise the building resilience in hot season. The effect of including a PCM layer into a ventilated roof is numerically analysed here in two different configurations: firstly, laid on the roof deck (PCM1 case) and, secondly, suspended in the middle of the ASV channel (PCM2 case). A computational fluid dynamics model was implemented to simulate airflow and heat transfer around and through the building envelope, under 3 days of extreme hot conditions in summer with high temperatures and low wind speed. Results showed slight differences in terms of mean temperatures at the different roof layers, although temperature fluctuations at deck in the PCM1 case were smaller than half of those estimated for the benchmark case. However, PCM2 configuration achieved a daily reduction of about 10 Wh/m2 (18%) in building energy load with respect to the benchmark case, whilst PCM1 got only 4% due to the lower ventilation at night time. Therefore, a suspended PCM layer in the ASV channel would be a better measure in terms of energy performance than laid on the deck surface, although this last option significantly decreases thermal stress of the insulation layer.
关键词： passive cooling technique,ventilated pitched roof,computational fluid dynamics,phase change material
更新于2025-09-23 15:19:57
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Prolonged Lifetime of Perovskite Solar Cells Using a Moisture-Blocked and Temperature-Controlled Encapsulation System Comprising a Phase Change Material as a Cooling Agent
摘要： Although the power conversion efficiency of perovskite solar cells (PSCs) reached up to 25% that made them comparable to the commercial solar cells, they are facing issues toward commercialization, especially their short lifetime. Remarkably, the most important key factors that regulate the durability of the devices are moisture, light, and heat. In this work, prolonging the device lifetime is focused by designing a flexible moisture-blocked and temperature-controlled encapsulation system. In this regard, a thermally adjusted phase change material is embedded in a polymer encapsulation layer to avoid the moisture diffusion, rapid temperature fluctuation, and undesired crystalline phase change of the perovskite layer in the PSCs under the operation condition. As a result, a 2 year stable device is achieved, whereas the reference device loses more than 50% of its performance after 10 days. Surprisingly, the charge transport resistance and recombination rate show no significant change during 450 days of storage, which confirms no increase in the defect density.
关键词： encapsulation system,temperature-controlled,phase change material,perovskite solar cells,lifetime,moisture-blocked
更新于2025-09-19 17:13:59
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Temperature dependent structural evolution and crystallization properties of thin Ge<sub>15</sub>Te<sub>85</sub> film revealed by in situ resistance, X-Ray diffraction and scanning electron microscopic studies
摘要： Chalcogenide-based Ge15Te85 thin films have recently been explored for Ovonic threshold switching (OTS) selector devices for vertically stackable cross-point memory applications. Despite reasonable understanding over its crystallization kinetics and threshold switching properties, the structural stability and morphological acquaintance at elevated temperatures remain key challenges. In this paper, we investigate the thermal stability, surface morphology and local structure of as-deposited amorphous Ge15Te85 thin film starting from room temperature up to 325 °C. Our experimental results reveal that upon heating, the de-vitrification is initiated in the form of localized segregation of Te atoms at 120 °C, followed by crystallization of Te at ~ 220 °C and GeTe at ~ 263 °C as corroborated by temperature- dependent measurements of electrical resistance, X-ray diffraction and scanning electron microscopic studies. Furthermore, the crystalline areas of these films are characterized by the fine-grained morphology, which clearly distinguishes the segregation of crystallization of Te and GeTe microstructures. These findings elucidate a deeper understanding of the multi-phase crystallization process through morphological evidence, which will be useful towards optimization of materials for Ovonic Threshold Switch (OTS) selector applications.
关键词： Chalcogenide thin films,phase change material,OTS Selector,Scanning electron microscopy,Ge15Te85
更新于2025-09-19 17:13:59
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Reversible Thermochromic Nanoparticles Composed of a Eutectic Mixture for Temperature-Controlled Photothermal Therapy
摘要： Photothermal therapy (PTT) is an effective approach for cancer therapy. However, the high temperature during the therapy increases the damage to surrounding normal tissues. Thermochromic material, which exhibits temperature-activated color change and optical absorption, is a promising photothermal agent for precisely temperature-controlled PTT. Nevertheless, the construction of nanosized thermochromic particles with appropriate transition temperature (44?47 oC) is still a great challenge. Here, thermochromic nanoparticles with transition temperature at 45 oC based on leuco dye-developer-solvent system are developed for thermostatic photothermal therapy of tumor. Below the temperature, the nanoparticles take a dark green color to absorb light and convert it into heat efficiently. Once the temperature reaches the transition point, the colored nanoparticles switch to colorless state, maintaining the temperature at the predefined level and allowing deeper light penetration. The auto-regulated nanoparticles exhibit prominent therapeutic effect for the tumor without destroying normal tissues.
关键词： temperature-controlled,thermochromic nanoparticles,phase-change material,photothermal,eutectic mixture
更新于2025-09-19 17:13:59
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Direct observation of elastic softening immediately after femtosecond-laser excitation in a phase-change material
摘要： The generation and propagation of photoexcited elastic waves in crystalline Ge2Sb2Te5 were analyzed by picosecond time-resolved x-ray diffraction using a femtosecond-laser pump and an x-ray free-electron laser probe technique. The crystalline lattice anisotropically expanded initially in approximately 20 ps after the excitation. This was followed by a periodic oscillation of the lattice strain. The elastic stiffness along the cubic [111] direction had significantly softened during the initial expansion, and the strain magnitude was the largest in the [100] and [110] directions. This indicates that femtosecond-laser excitation creates a shallower interlayer potential between the Te and Ge-Sb layers and eventually leads to softening of the elastic stiffness along the cubic [111] direction. Furthermore, this softened state increases the system’s sensitivity to an external stress field. This residual internal stress in a thin film enhances the selective formation of a particular type of variant during the symmetry change from cubic to rhombohedra. This causes the subsequent anisotropic expansion. These phenomena are quite interesting and align with the ultrafast amorphization of this material.
关键词： elastic stiffness,femtosecond-laser excitation,elastic waves,x-ray diffraction,phase-change material
更新于2025-09-16 10:30:52
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Photovoltaic panel integrated with phase change materials (PV-PCM): technology overview and materials selection
摘要： In recent years, the utilization of phase change materials (PCMs) in photovoltaic (PV) module for thermal regulation has attracted wide attention in this field, as the hybrid PV-PCM technology can not only achieve higher photoelectric conversion efficiency but also make it possible to extract thermal energy stored in PCMs for cascade utilization. Although substantial research has been carried out on PV-PCM systems, the promise of practical application is still far from clear with some barriers unsolved, such as PCMs which need further improvements in both technical and economical view. In this paper, a comprehensive literature review of the state-of-the-art aspects of PV-PCM systems is presented, with the focus on technology overview and materials selection. The concept of hybrid PV-PCM system is first discussed with its general configuration and energy balance, to figure out the key factors affecting its performance. Besides, the development route of PV-PCM research is outlined through a comprehensive review of 104 research articles during 2004–2018, clarifying the representative achievements and existing problems in each stage. Furthermore, PCMs are highlighted in this paper with details on their classification, properties, and application in previous PV-PCM research. In particular a triangle about materials selection criteria and determination strategy of phase transition temperature is proposed. Finally, the challenges and prospects of future research on PV-PCM systems are raised, advocating that more attention should be addressed on new strategies to overcome the existing problems such as insufficient reliability and economic feasibility.
关键词： Phase change material (PCM),PV cooling,PV-PCM,Solar photovoltaic (PV),Review
更新于2025-09-16 10:30:52
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Experimental study conducted for the identification of best heat absorption and dissipation methodology in solar photovoltaic panel
摘要： The solar PV technology has become a significant alternative for conventional fossil fuel resources. The recent researches are focusing on techniques to increase the efficiency of the solar photovoltaic (PV) systems to address the growing needs of the global electricity demand. Maintaining the PV panel temperature according to the specified standard helps in harnessing the optimal power output consistently. Although there are various PV panel cooling techniques available in the existing literature, there is always a huge expectation among the energy sectors in terms of rising the efficiency value, as well as lowering the cost of investment. In this aspect, the proposed method provides the best solution by improving the efficiency of the solar photovoltaic panel by regulating the temperature using a material called as the Phase Change Material which is entrenched with an external finned heat sink to improve the thermal conductivity of the material PCM. In this work, the concept is investigated by an experimental setup under direct sun rays in the natural environmental conditions for four different cases (Case A, Case B, Case C, and Case D). The concept of temperature regulation is recorded through FLIR thermal imaging camera and the observations are presented. After thorough experimental investigations of all the four cases, it is found that PCM entrenched with heatsink (Case D) can certainly be an efficient approach to drop the operating temperature of the PV panel with lowest cost and enhance the efficiency of the PV panel to the maximum extent.
关键词： Phase change material,Solar photovoltaic (PV) panel,Heat sink,FLIR thermal images
更新于2025-09-16 10:30:52
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Experimental study on the performance of a solar photovoltaic/thermal system combined with phase change material
摘要： We present a comprehensive analysis of a solar photovoltaic/thermal system combined with phase change material, i.e., a PV/T-PCM system. A fatty acid was chosen as the PCM with a phase transition temperature of 37 °C. A solar collector filled with PCM, which contained rectangular metal fins to enhance heat transfer, was used to cool the PV. Four-day experimental measurements were carried out under real outdoor climatic conditions in Shanghai, China. During the experiment, we examined two different intermittent thermal regulation strategies using a water circulation loop in the PV/T-PCM system to improve the overall solar energy utilization efficiency, and detailed comparisons were performed. The results indicated that the use of PCM in the solar collector could significantly mitigate the temperature fluctuation of the PV panel and improve the photoelectric efficiency. Due to the low thermal conductivity of fatty acid, the temperature stratification in the solar collector was still significant even with the addition of metal copper fins. The thermal regulation strategy of setting the temperature at 45 °C gave better performance and the overall efficiencies of Case 1 and Case 3 could reach approximately 91%. The overall efficiency of Case 3 and Case 4 was approximately 85% with the thermal regulation strategy of setting the temperature at 50 °C. More heat could be removed from the PCM in the solar collector using the relatively low temperature setting of the thermal regulation strategy. It was concluded that the overall energy utilization ratio of the PV/T-PCM system can be improved through a reasonable thermal regulation strategy; however, further work on the economics analysis of the system is still needed.
关键词： Phase change material,Photovoltaic/thermal system,Dual-axis tracker,Photoelectric efficiency,Photothermal efficiency
更新于2025-09-16 10:30:52