condensed_matter_physics (2)

2D MXenes...

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Helper two-dimensional metal-carbide layers could improve perovskite solar cell stability and help make these complex solar cells a viable green energy option. Credit: iStock Milos-Muller

 

Topics: Condensed Matter Physics, Green Tech, Materials Science, Metamaterials, Nanotechnology, Solar Power


With the reality of climate change looming, the importance of realistic green energy sources is higher than ever. Solar cells are one promising avenue, as they can convert readily available visible and ultraviolet energy into usable electricity. In particular, perovskite materials sandwiched between other support layers have demonstrated impressive power conversion efficiencies. Current challenges reside in optimizing perovskite/support layer interfaces, which can directly impact power conversion and cell degradation. Researchers Antonio Agresti et al. under the direction of Aldo Di Carlo at the University of Rome Tor Vergata in Italy have investigated how cells containing two-dimensional titanium-carbide MXene support layers could improve perovskite solar cell performance.

To obtain good power conversion within a perovskite solar cell, all layers and layer interfaces within the cell must have good compatibility. Typical cells contain the active perovskite material sandwiched between two charge transport layers, which are then adjacent to their corresponding electrodes. Support layers may also be added. Charge mobility, energy barriers, interface energy alignment, and interfacial vacancies all impact compatibility and subsequent cell performance and stability. Thus, engineering well-suited interfaces with the cell is paramount to cell success and long-term stability, an important criterion for potential commercialization.

Two-dimensional buffer materials could help to modify and promote useful interface interactions. MXenes, a growing class of two-dimensional transitional metal carbides, nitrides, and carbonitrides, have shown impressive electronic properties that are easily tuned via surface modification. For example, the band gap of an MXene can be modified by changing the surface termination group from an oxygen atom to a hydroxide molecule. Additionally, MXene composition impacts the overall material performance. This type of fine-tuning allows impressive control over MXene properties and makes them ideal for interface adjustments.

 

Two-dimensional MXenes improve perovskite solar cell efficiency
Amanda Carr, Physics World

#P4TC: MXenes...August 24, 2015

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Super State...

Super state: three independent groups have caught sight of supersolidity. (Courtesy: iStock/3quarks)

 

Topics: Bose-Einstein Condensate, Condensed Matter Physics, Electromagnetism, Quantum Mechanics


Atomic systems that behave very much like supersolids have been created independently by teams of physicists in Italy, Germany have Austria. The teams have shown that dipolar quantum gases trapped by magnetic fields can spontaneously separate into arrays of coherent droplets, providing a system closer to the original conception of a supersolid.


The supersolid phase is a counterintuitive quantum state of matter that has both crystalline order and frictionless flow at very low temperatures. The phenomenon is related to superfluidity and was predicted 50 years ago by Soviet physicists Alexander Andreev and Ilya Lifschitz. However, supersolidity has proved frustratingly difficult to observe.

In a superfluid, the energy required to create a density modulation generally increases as the modulation’s wavelength gets shorter. At one characteristic wavelength, however, the energy takes a sudden dip – much as waves pass more easily through a crystal when the wavelength equals the separation between the atoms. If the superfluid were cold enough, Andreev and Lifschitz reasoned, the energy required would drop to zero at this wavelength. The superfluid would then spontaneously separate into tiny droplets, effectively forming an ordered crystal.

 

Supersolid behavior spotted in dipolar quantum gases, Tim Wogan, Physics World

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