3 research outputs found
Unraveling the Characteristic Shape for Magnetic Field Effects in PolymerâFullerene Solar Cells
Spin-dependent
effects in organic solar cells (OSCs) are responsible
for tuning the electric current when an external magnetic field is
applied. Here, we report the magnetic field effect (MFE) on wide-bandgap
(WBG) solar cells based on the polymers PBDTÂ(O)-T1 and PBDTÂ(Se)-T1
blended with PC<sub>70</sub>BM. Furthermore, we propose an experimental
method based on the electrical transport (<i>i</i>â<i>V</i>) measurements to unveil the negative magneto conductance
(MC) at small bias. The observed curves in a double-logarithmic scale
display a particular S-like shape, independent of the OSC power conversion
efficiency (PCE) or MC amplitudes. Additionally, from the slope of
the S-like shape curve, it is possible to identify the fullerene concentrations
that would result in the minimum MC and the maximum PCE. Our work
opens up a door to find more patterns to describe MFE and PCE in polymerâfullerene
solar cells, without the application of external magnetic or luminous
sources
Skyrmions in Magnetic Tunnel Junctions
In
this work, we demonstrate that skyrmions can be nucleated in the free
layer of a magnetic tunnel junction (MTJ) with DzyaloshinskiiâMoriya
interactions (DMIs) by a spin-polarized current with the assistance
of stray fields from the pinned layer. The size, stability, and number
of created skyrmions can be tuned by either the DMI strength or the
stray field distribution. The interaction between the stray field
and the DMI effective field is discussed. A device with multilevel
tunneling magnetoresistance is proposed, which could pave the ways
for skyrmionâMTJ-based multibit storage and artificial neural
network computation. Our results may facilitate the efficient nucleation
and electrical detection of skyrmions
Epitaxial Growth of Aligned and Continuous Carbon Nanofibers from Carbon Nanotubes
Exploiting the superior properties
of nanomaterials at macroscopic scale is a key issue of nanoscience.
Different from the integration strategy, âadditive synthesisâ
of macroscopic structures from nanomaterial templates may be a promising
choice. In this paper, we report the epitaxial growth of aligned,
continuous, and catalyst-free carbon nanofiber thin films from carbon
nanotube films. The fabrication process includes thickening of continuous
carbon nanotube films by gas-phase pyrolytic carbon deposition and
further graphitization of the carbon layer by high-temperature treatment.
As-fabricated nanofibers in the film have an âannual ringâ
cross-section, with a carbon nanotube core and a graphitic periphery,
indicating the templated growth mechanism. The absence of a distinct
interface between the carbon nanotube template and the graphitic periphery
further implies the epitaxial growth mechanism of the fiber. The mechanically
robust thin film with tunable fiber diameters from tens of nanometers
to several micrometers possesses low density, high electrical conductivity,
and high thermal conductivity. Further extension of this fabrication
method to enhance carbon nanotube yarns is also demonstrated, resulting
in yarns with âŒ4-fold increased tensile strength and âŒ10-fold
increased Youngâs modulus. The aligned and continuous features
of the films together with their outstanding physical and chemical
properties would certainly promote the large-scale applications of
carbon nanofibers