5 research outputs found
Flexible Solar Cells Using Doped Crystalline Si Film Prepared by Self-Biased Sputtering Solid Doping Source in SiCl<sub>4</sub>/H<sub>2</sub> Microwave Plasma
We developed an innovative approach
of self-biased sputtering solid doping source process to synthesize
doped crystalline Si film on flexible polyimide (PI) substrate via
microwave-plasma-enhanced chemical vapor deposition (MWPECVD) using
SiCl<sub>4</sub>/H<sub>2</sub> mixture. In this process, P dopants
or B dopants were introduced by sputtering the solid doping target
through charged-ion bombardment in situ during high-density microwave
plasma deposition. A strong correlation between the number of solid
doping targets and the characteristics of doped Si films was investigated
in detail. The results show that both P- and B-doped crystalline Si
films possessed a dense columnar structure, and the crystallinity
of these structures decreased with increasing the number of solid
doping targets. The films also exhibited a high growth rate (>4.0
nm/s). Under optimal conditions, the maximum conductivity and corresponding
carrier concentration were, respectively, 9.48 S/cm and 1.2 Ă—
10<sup>20</sup> cm<sup>–3</sup> for P-doped Si film and 7.83
S/cm and 1.5 × 10<sup>20</sup> cm<sup>–3</sup> for B-doped
Si film. Such high values indicate that the incorporation of dopant
with high doping efficiency (around 40%) into the Si films was achieved
regardless of solid doping sources used. Furthermore, a flexible crystalline
Si film solar cell with substrate configuration was fabricated by
using the structure of PI/Mo film/<i>n</i>-type Si film/<i>i</i>-type Si film/<i>p</i>-type Si film/ITO film/Al
grid film. The best solar cell performance was obtained with an open-circuit
voltage of 0.54 V, short-circuit current density of 19.18 mA/cm<sup>2</sup>, fill factor of 0.65, and high energy conversion of 6.75%.
According to the results of bending tests, the critical radius of
curvature (<i>R</i><sub>C</sub>) was 12.4 mm, and the loss
of efficiency was less than1% after the cyclic bending test for 100
cycles at <i>R</i><sub>C</sub>, indicating superior flexibility
and bending durability. These results represent important steps toward
a low-cost approach to high-performance flexible crystalline Si film-based
photovoltaic devices
High Mobility of Graphene-Based Flexible Transparent Field Effect Transistors Doped with TiO<sub>2</sub> and Nitrogen-Doped TiO<sub>2</sub>
Graphene
with carbon atoms bonded in a honeycomb lattice can be
tailored by doping various species to alter the electrical properties
of the graphene for fabricating p-type or n-type field-effect transistors
(FETs). In this study, large-area and single-layer graphene was grown
on electropolished Cu foil using the thermal chemical vapor deposition
method; the graphene was then transferred onto a polyÂ(ethylene terephthalate)
(PET) substrate to produce flexible, transparent FETs. TiO<sub>2</sub> and nitrogen-doped TiO<sub>2</sub> (N-TiO<sub>2</sub>) nanoparticles
were doped on the graphene to alter its electrical properties, thereby
enhancing the carrier mobility and enabling the transistors to sense
UV and visible light optically. The results indicated that the electron
mobility of the graphene was 1900 cm<sup>2</sup>/(V·s). Dopings
of TiO<sub>2</sub> and N-doped TiO<sub>2</sub> (1.4 at. % N) lead
to n-type doping effects demonstrating extremely high carrier mobilities
of 53000 and 31000 cm<sup>2</sup>/(V·s), respectively. Through
UV and visible light irradiation, TiO<sub>2</sub> and N-TiO<sub>2</sub> generated electrons and holes; the generated electrons transferred
to graphene channels, causing the FETs to exhibit n-type electric
behavior. In addition, the Dirac points of the graphene recovered
to their original state within 5 min, confirming that the graphene-based
FETs were photosensitive to UV and visible light. In a bending state
with a radius of curvature greater than 2.0 cm, the carrier mobilities
of the FETs did not substantially change, demonstrating the application
possibility of the fabricated graphene-based FETs in photosensors
Hollow Few-Layer Graphene-Based Structures from Parafilm Waste for Flexible Transparent Supercapacitors and Oil Spill Cleanup
We
report a versatile strategy to exploit parafilm waste as a carbon
precursor for fabrication of freestanding, hollow few-layer graphene
fiber mesh (HFGM) structures without use of any gaseous carriers/promoters
via an annealing route. The freestanding HFGMs possess good mechanical
flexibility, tailorable transparency, and high electrical conductivity,
consequently qualifying them as promising electrochemical electrodes.
Because of the hollow spaces, electrolyte ions can easily access into
and contact with interior surfaces of the graphene fibers, accordingly
increasing electrode/electrolyte interfacial area. As expected, solid-state
supercapacitors based on the HFGMs exhibit a considerable enhancement
in specific capacitance (20–30 fold) as compared to those employing
chemical vapor deposition compact graphene films. Moreover, the parafilm
waste is found to be beneficial for one-step fabrication of nanocarbon/few-layer
graphene composite meshes with superior electrochemical performance,
outstanding superhydrophobic property, good self-cleaning ability,
and great promise for oil spill cleanup
Hollow Few-Layer Graphene-Based Structures from Parafilm Waste for Flexible Transparent Supercapacitors and Oil Spill Cleanup
We
report a versatile strategy to exploit parafilm waste as a carbon
precursor for fabrication of freestanding, hollow few-layer graphene
fiber mesh (HFGM) structures without use of any gaseous carriers/promoters
via an annealing route. The freestanding HFGMs possess good mechanical
flexibility, tailorable transparency, and high electrical conductivity,
consequently qualifying them as promising electrochemical electrodes.
Because of the hollow spaces, electrolyte ions can easily access into
and contact with interior surfaces of the graphene fibers, accordingly
increasing electrode/electrolyte interfacial area. As expected, solid-state
supercapacitors based on the HFGMs exhibit a considerable enhancement
in specific capacitance (20–30 fold) as compared to those employing
chemical vapor deposition compact graphene films. Moreover, the parafilm
waste is found to be beneficial for one-step fabrication of nanocarbon/few-layer
graphene composite meshes with superior electrochemical performance,
outstanding superhydrophobic property, good self-cleaning ability,
and great promise for oil spill cleanup
Au@Cu<sub>2</sub>O Core–Shell and Au@Cu<sub>2</sub>Se Yolk–Shell Nanocrystals as Promising Photocatalysts in Photoelectrochemical Water Splitting and Photocatalytic Hydrogen Production
In this work, we demonstrated the practical use of Au@Cu2O core–shell and Au@Cu2Se yolk–shell
nanocrystals
as photocatalysts in photoelectrochemical (PEC) water splitting and
photocatalytic hydrogen (H2) production. The samples were
prepared by conducting a sequential ion-exchange reaction on a Au@Cu2O core–shell nanocrystal template. Au@Cu2O and Au@Cu2Se displayed enhanced charge separation as
the Au core and yolk can attract photoexcited electrons from the Cu2O and Cu2Se shells. The localized surface plasmon
resonance (LSPR) of Au, on the other hand, can facilitate additional
charge carrier generation for Cu2O and Cu2Se.
Finite-difference time-domain simulations were carried out to explore
the amplification of the localized electromagnetic field induced by
the LSPR of Au. The charge transfer dynamics and band alignment of
the samples were examined with time-resolved photoluminescence and
ultraviolet photoelectron spectroscopy. As a result of the improved
interfacial charge transfer, Au@Cu2O and Au@Cu2Se exhibited a substantially larger photocurrent of water reduction
and higher photocatalytic activity of H2 production than
the corresponding pure counterpart samples. Incident photon-to-current
efficiency measurements were conducted to evaluate the contribution
of the plasmonic effect of Au to the enhanced photoactivity. Relative
to Au@Cu2O, Au@Cu2Se was more suited for PEC
water splitting and photocatalytic H2 production by virtue
of the structural advantages of yolk–shell architectures. The
demonstrations from the present work may shed light on the rational
design of sophisticated metal–semiconductor yolk–shell
nanocrystals, especially those comprising metal selenides, for superior
photocatalytic applications