17 research outputs found
An 8.68% Efficiency Chemically-Doped-Free Graphene–Silicon Solar Cell Using Silver Nanowires Network Buried Contacts
Graphene–silicon
(Gr-Si) heterojunction solar cells have
been recognized as one of the most low-cost candidates in photovoltaics
due to its simple fabrication process. However, the high sheet resistance
of chemical vapor deposited (CVD) Gr films is still the most important
limiting factor for the improvement of the power conversion efficiency
of Gr-Si solar cells, especially in the case of large device-active
area. In this work, we have fabricated a novel transparent conductive
film by hybriding a monolayer Gr film with silver nanowires (AgNWs)
network soldered by the graphene oxide (GO) flakes. This Gr-AgNWs
hybrid film exhibits low sheet resistance and larger direct-current
to optical conductivity ratio, quite suitable for solar cell fabrication.
An efficiency of 8.68% has been achieved for the Gr-AgNWs-Si solar
cell, in which the AgNWs network acts as buried contacts. Meanwhile,
the Gr-AgNWs-Si solar cells have much better stability than the chemically
doped Gr-Si solar cells. These results show a new route for the fabrication
of high efficient and stable Gr-Si solar cells
Silver Nanoshell Plasmonically Controlled Emission of Semiconductor Quantum Dots in the Strong Coupling Regime
Strong
coupling between semiconductor excitons and localized surface
plasmons (LSPs) giving rise to hybridized plexciton states in which
energy is coherently and reversibly exchanged between the components
is vital, especially in the area of quantum information processing
from fundamental and practical points of view. Here, in photoluminescence
spectra, rather than from common extinction or reflection measurements,
we report on the direct observation of Rabi splitting of approximately
160 meV as an indication of strong coupling between excited states
of CdSe/ZnS quantum dots (QDs) and LSP modes of silver nanoshells
under nonresonant nanosecond pulsed laser excitation at room temperature.
The strong coupling manifests itself as an anticrossing-like behavior
of the two newly formed polaritons when tuning the silver nanoshell
plasmon energies across the exciton line of the QDs. Further analysis
substantiates the essentiality of high pump energy and collective
strong coupling of many QDs with the radiative dipole mode of the
metallic nanoparticles for the realization of strong coupling. Our
finding opens up interesting directions for the investigation of strong
coupling between LSPs and excitons from the perspective of radiative
recombination under easily accessible experimental conditions
Chemical Vapor Deposition of Graphene on Self-Limited SiC Interfacial Layers Formed on Silicon Substrates for Heterojunction Devices
Direct
chemical vapor deposition (CVD) of graphene on any desired
substrate is always required to manufacture high-quality heterojunctions
with excellent interfacial properties. Herein, the growth of graphene
on cubic-silicon carbide (3C-SiC) surfaces using conventional high-temperature
direct thermal CVD and plasma-enhanced CVD (PECVD) is explored, which
is hardly reported to date. Since 3C-SiC substrates are not available,
the controlled self-limited 3C-SiC layers on the Si(100) substrates
were grown at different temperatures (900–1200 °C) via
thermal-CVD technique to obtain virtual 3C-SiC substrates. The direct
production of graphene via thermal CVD could not be achieved on such
3C-SiC surfaces. The density functional theory and molecular dynamics
simulations confirm that the carbon atom diffusion over the 3C-SiC
surface is extremely low, like over the Si surface, which leads to
no graphene growth. A similar growth mechanism may be attributed to
their similar crystal structure viz diamond cubic for Si and zinc
blend for 3C-SiC. However, graphene nanowalls (GNWs) were successfully
grown on both Si and 3C-SiC/Si surfaces at 700 °C via the PECVD
technique, where similar surface morphologies were observed because
the growth mechanism of GNWs is independent of substrate type. Moreover, I–V characterization was performed
for different SiC/Si heterostructures and their corresponding GNWs/SiC/Si
heterostructures, respectively. The current conduction improved considerably
more for GNW/SiC/Si heterostructures as compared to SiC/Si heterostructures,
but the creation of a SiC interfacial layer as well as its quality
affected the conductivity of GNWs/SiC/Si heterostructures. The inevitable
formation of an interfacial SiC layer during the direct graphene growth
via thermal CVD on Si substrates can seriously affect the performance
of graphene/Si heterojunction devices. Hence, PECVD growth of graphene
is an ideal option to fabricate graphene/Si heterojunction devices
with excellent interfacial properties or graphene/3C-SiC/Si heterojunction
devices for various electronic/optoelectronic applications such as
gas sensors and photovoltaic devices
Epitaxial Growth of Twinned Au–Pt Core–Shell Star-Shaped Decahedra as Highly Durable Electrocatalysts
Pt epitaxial layer on a nanoparticle
with twinned structure and well-defined shape is highly desirable
in order to achieve high performance in both catalytic activity and
durability toward oxygen reduction reaction (ORR). However, it remains
tremendously challenging to produce conformal, heterogeneous, twinned
nanostructures due to the high internal strain and surface energy
of Pt. In addition, these twinned nanostructures may be subject to
degradation in highly corrosive ORR environments due to the high energy
of twin boundary. Here we report the synthesis of Au–Pt core–shell
star-shaped decahedra bounded mainly by {111} facets, in which Pt
shells with controlled thickness epitaxially grew on Au cores with
a 5-fold twinned structure. The incorporation of the amine group decreases
the surface energy of Pt by strong adsorption and thus facilitates
the epitaxial growth of Pt on Au core instead of the dendritic growth.
In addition, Br<sup>–</sup> ion could largely stabilize the
{111} facets of Pt, which prevent the formation of spherical nanoparticles.
The Au–Pt core–shell decahedra with thicker Pt shell
exhibited enhanced ORR properties in terms of activity and durability.
Specifically, AuPt<sub>1.03</sub> star-shaped decahedra achieved the
highest mass activity (0.94 mA/μg<sub>Pt</sub>) and area activity
(1.09 mA/cm<sup>2</sup><sub>Pt</sub>), which is ∼6.7 and 5
times, respectively, as high as those of the commercial Pt/C (ETEK).
Significantly, such star-shaped decahedra were highly stable with
∼10% loss in area activity and ∼20% loss in mass activity
after 30 000 CV cycles in O<sub>2</sub> saturated acid solution
Ambient Engineering for High-Performance Organic–Inorganic Perovskite Hybrid Solar Cells
Considering the evaporation of solvents
during fabrication of perovskite films, the organic ambience will
present a significant influence on the morphologies and properties
of perovskite films. To clarify this issue, various ambiences of <i>N</i>,<i>N</i>-dimethylformamide (DMF), dimethyl sulfoxide
(DMSO), and chlorobenzene (CBZ) are introduced during fabrication
of perovskite films by two-step sequential deposition method. The
results reveal that an ambient CBZ atmosphere is favorable to control
the nucleation and growth of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> grains while the others present a negative effect. The statistical
results show that the average efficiencies of perovskite solar cells
processed in an ambient CBZ atmosphere can be significantly improved
by a relatively average value of 35%, compared with those processed
under air. The efficiency of the best perovskite solar cells can be
improved from 10.65% to 14.55% by introducing this ambience engineering
technology. The CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> film with
large-size grains produced in an ambient CBZ atmosphere can effectively
reduce the density of grain boundaries, and then the recombination
centers for photoinduced carriers. Therefore, a higher short-circuit
current density is achieved, which makes main contribution to the
improvement in efficiency. These results provide vital progress toward
understanding the role of ambience in the realization of highly efficient
perovskite solar cells
Multistage Transformation and Lattice Fluctuation at AgCl–Ag Interface
Solid-state
transformation between different materials is often
accompanied by mechanical expansion and compression due to their volume
change and structural evolution at interfaces. However, these two
types of dynamics are usually difficult to monitor in the same time.
In this work, we use in situ transmission electron microscopy to directly
study the reduction transformation at the AgCl–Ag interface.
Three stages of lattice fluctuations were identified and correlated
to the structural evolution. During the steady state, a quasi-layered
growth mode of Ag in both vertical and lateral directions were observed
due to the confinement of AgCl lattices. The development of planar
defects and depletion of AgCl are respectively associated with lattice
compression and relaxation. Topography and structure of decomposing
AgCl was further monitored by in situ scanning transmission electron
microscopy. Silver species are suggested to originate from both the
surface and the interior of AgCl, and be transported to the interface.
Such mass transport may have enabled the steady state and lattice
compression in this volume-shrinking transformation
Multistage Transformation and Lattice Fluctuation at AgCl–Ag Interface
Solid-state
transformation between different materials is often
accompanied by mechanical expansion and compression due to their volume
change and structural evolution at interfaces. However, these two
types of dynamics are usually difficult to monitor in the same time.
In this work, we use in situ transmission electron microscopy to directly
study the reduction transformation at the AgCl–Ag interface.
Three stages of lattice fluctuations were identified and correlated
to the structural evolution. During the steady state, a quasi-layered
growth mode of Ag in both vertical and lateral directions were observed
due to the confinement of AgCl lattices. The development of planar
defects and depletion of AgCl are respectively associated with lattice
compression and relaxation. Topography and structure of decomposing
AgCl was further monitored by in situ scanning transmission electron
microscopy. Silver species are suggested to originate from both the
surface and the interior of AgCl, and be transported to the interface.
Such mass transport may have enabled the steady state and lattice
compression in this volume-shrinking transformation
Light-Emitting Diodes Based on Colloidal Silicon Quantum Dots with Octyl and Phenylpropyl Ligands
Colloidal silicon
quantum dots (Si QDs) hold ever-growing promise
for the development of novel optoelectronic devices such as light-emitting
diodes (LEDs). Although it has been proposed that ligands at the surface
of colloidal Si QDs may significantly impact the performance of LEDs
based on colloidal Si QDs, little systematic work has been carried
out to compare the performance of LEDs that are fabricated using colloidal
Si QDs with different ligands. Here, colloidal Si QDs with rather
short octyl ligands (Octyl-Si QDs) and phenylpropyl ligands (PhPr-Si
QDs) are employed for the fabrication of LEDs. It is found that the
optical power density of PhPr-Si QD LEDs is larger than that of Octyl-Si
QD LEDs. This is due to the fact that the surface of PhPr-Si QDs is
more oxidized and less defective than that of Octyl-Si QDs. Moreover,
the benzene rings of phenylpropyl ligands significantly enhance the
electron transport of QD LEDs. It is interesting that the external
quantum efficiency (EQE) of PhPr-Si QD LEDs is lower than that of
Octyl-Si QD LEDs because the benzene rings of phenylpropyl ligands
suppress the hole transport of QD LEDs. The unbalance between the
electron and hole injection in PhPr-Si QD LEDs is more serious than
that in Octyl-Si QD LEDs. The currently obtained highest optical power
density of ∼0.64 mW/cm<sup>2</sup> from PhPr-Si QD LEDs and
highest EQE of ∼6.2% from Octyl-Si QD LEDs should encourage
efforts to further advance the development of high-performance optoelectronic
devices based on colloidal Si QDs
Multistage Transformation and Lattice Fluctuation at AgCl–Ag Interface
Solid-state
transformation between different materials is often
accompanied by mechanical expansion and compression due to their volume
change and structural evolution at interfaces. However, these two
types of dynamics are usually difficult to monitor in the same time.
In this work, we use in situ transmission electron microscopy to directly
study the reduction transformation at the AgCl–Ag interface.
Three stages of lattice fluctuations were identified and correlated
to the structural evolution. During the steady state, a quasi-layered
growth mode of Ag in both vertical and lateral directions were observed
due to the confinement of AgCl lattices. The development of planar
defects and depletion of AgCl are respectively associated with lattice
compression and relaxation. Topography and structure of decomposing
AgCl was further monitored by in situ scanning transmission electron
microscopy. Silver species are suggested to originate from both the
surface and the interior of AgCl, and be transported to the interface.
Such mass transport may have enabled the steady state and lattice
compression in this volume-shrinking transformation
In situ Study of Oxidative Etching of Palladium Nanocrystals by Liquid Cell Electron Microscopy
Oxidative etching
has widely prevailed in the synthesis of a crystal
and played a critical role in determining the final growth behavior.
In this Letter, we report an in situ microscopic study on the oxidative
etching of palladium cubic nanocrystals by liquid cell scanning transmission
electron microscopy. The etching was realized with oxidative radiation
reactants from electron–water interaction in the presence of
Br<sup>–</sup> ions. Dissolution dynamics of monodispersed
and aggregated nanocrystals were both investigated and compared. Analyses
on the dissolution kinetics of nanocrystals and the diffusion kinetics
of the dissolved agents were carried out based on the scanning transmission
electron microscopy characterizations. The results presented here
pave a way toward the quantitative understanding of the oxidative
etching reaction and its application in the functionally orientated
fabrication of nanocrystals with certain sizes, structures, and morphologies