78 research outputs found
Оптичні характеристики тонких плівок SnO2 як сонячних елементів, досліджених методом кутової спектроскопічної еліпсометрії
У даній роботі методом розпилювального піролізу отримано наноструктуру ТСО в тонкій плівці оксиду олова. Різні параметри осадження були встановлені та оптимізовані для приготування вихідного
розчину з дигідрату хлориду олова, нанесеного на очищену скляну підкладку. Була досягнута характеристика тонкого шару чистого оксиду олова, нанесеного методом конденсації. Методом рентгенівської
дифрактометрії показано, що плівка оксиду олова полікристалічна з тетрагональною структурою, яка
складається в основному з орієнтацій (101), (211) та інших менш інтенсивних. Ультрафіолетова спектроскопія підтвердила високу прозорість тонкого шару чистого SnO2 з пропусканням 95 % при 600 нм.
Величина оптичної щілини осадженого зразка дорівнює 3,95 еВ. Спектроскопічні еліпсометричні вимірювання параметрів Psi і delta були проведені під різними кутами падіння 65°, 70° і 75°. Оптичну постійну шару SnO2 було змодельовано за допомогою B-сплайнової моделі. Достовірність еліпсометричного
підгонки визначена при куті падіння 75°, що вказує на мінімальний MSE, рівний 4,022. Результати SE
характеристики тонкої плівки SnO2 на скляній підкладці показали, що товщина шару, показник заломлення та коефіцієнт екстинкції дорівнюють 219,78 нм, 1,41 та 0,123 відповідно. Отримані структурні
та оптичні параметри підтвердили, що утворився тонкий шар SnO2. Цей шар продемонстрував широку
смугу пропускання та високу прозорість типу напівпровідника TCO, який можна використовувати як
антибліковий шар в сонячних елементах.In this work, we prepared a nanostructure of TCO in a thin film of tin oxide using the spray pyrolysis
method. The different deposition parameters have been set and optimized to prepare the source solution
from Tin chloride dihydrate deposited on a cleaned glass substrate. The characterization of the thin layer of
pure tin oxide deposited by spraying was achieved. The X-ray diffractometer shows that the tin oxide film is
polycrystalline with a tetragonal structure, which consists mainly of orientations (101), (211) and other less
intense. Ultra-violet-spectroscopy approved an excellent transparency of the thin layer of pure SnO2 with a
transmission of 95 % at 600 nm. The optical gap value of the deposited sample is equal to 3.95 eV. The
spectroscopic ellipsometry measurements of the Psi and delta parameters were carried out at various angles
of incidence 65°, 70° and 75°. The optical constant of the SnO2 layer was modeled using a B-spline model.
The goodness of the ellipsometric fitting was found at an incidence angle of 75°, which indicates a minimum
MSE equal to 4.022. The SE characterization results of SnO2 thin film on the glass substrate have shown
that the layer thickness, the refractive index and the extinction coefficient are equal to 219.78 nm, 1.41 and
0.123, respectively. The resulting structural and optical parameters confirmed that a thin SnO2 layer was
formed. This layer showed a wide bandwidth and high transparency of a type of TCO semiconductor, which
can be used as an anti-reflective layer in solar cell devices
Correlation between Photoinduced Electron Transfer and Photovoltaic Characteristics in Solar Cells Based on Hybrid Core−Shell Nanoparticles
Improving Light Harvesting in Dye-Sensitized Solar Cells Using Hybrid Bimetallic Nanostructures
In this work we demonstrate improved
light trapping in dye-sensitized
solar cells (DSSCs) with hybrid bimetallic gold core/silver shell
nanostructures. Silica-coated bimetallic nanostructures (Au/Ag/SiO<sub>2</sub> NSs) integrated in the active layer of DSSCs resulted in
7.51% power conversion efficiency relative to 5.97% for reference
DSSCs, giving rise to 26% enhancement in device performance. DSSC
efficiencies were governed by the particle density of Au/Ag/SiO<sub>2</sub> NSs with best performing devices utilizing only 0.44 wt %
of nanostructures. We performed transient absorption spectroscopy
of DSSCs with variable concentrations of Au/Ag/SiO<sub>2</sub> NSs
and observed an increase in amplitude and decrease in lifetime with
increasing particle density relative to reference. We attributed this
trend to plasmon resonant energy transfer and population of the singlet
excited states of the sensitizer molecules at the optimum concentration
of NSs promoting enhanced exciton generation and rapid charge transfer
into TiO<sub>2</sub>
Digital Transfer Growth of Patterned 2D Metal Chalcogenides by Confined Nanoparticle Evaporation
Developing methods for the facile synthesis of two-dimensional (2D) metal chalcogenides and other layered materials is crucial for emerging applications in functional devices. Controlling the stoichiometry, number of the layers, crystallite size, growth location, and areal uniformity is challenging in conventional vapor-phase synthesis. Here, we demonstrate a method to control these parameters in the growth of metal chalcogenide (GaSe) and dichalcogenide (MoSe<sub>2</sub>) 2D crystals by precisely defining the mass and location of the source materials in a confined transfer growth system. A uniform and precise amount of stoichiometric nanoparticles are first synthesized and deposited onto a substrate by pulsed laser deposition (PLD) at room temperature. This <i>source</i> substrate is then covered with a <i>receiver</i> substrate to form a confined vapor transport growth (VTG) system. By simply heating the source substrate in an inert background gas, a natural temperature gradient is formed that evaporates the confined nanoparticles to grow large, crystalline 2D nanosheets on the cooler receiver substrate, the temperature of which is controlled by the background gas pressure. Large monolayer crystalline domains (∼100 μm lateral sizes) of GaSe and MoSe<sub>2</sub> are demonstrated, as well as continuous monolayer films through the deposition of additional precursor materials. This PLD–VTG synthesis and processing method offers a unique approach for the controlled growth of large-area metal chalcogenides with a controlled number of layers in patterned growth locations for optoelectronics and energy related applications
Vibrational Dynamics of Interfacial Water by Free Induction Decay Sum Frequency Generation (FID-SFG) at the Al 2
Ultrafast Charge Transfer and Hybrid Exciton Formation in 2D/0D Heterostructures
Photoinduced interfacial charge transfer
is at the heart of many
applications, including photovoltaics, photocatalysis, and photodetection.
With the emergence of a new class of semiconductors, i.e., monolayer
two-dimensional transition metal dichalcogenides (2D-TMDs), charge
transfer at the 2D/2D heterojunctions has attracted several efforts
due to the remarkable optical and electrical properties of 2D-TMDs.
Unfortunately, in 2D/2D heterojunctions, for a given combination of
two materials, the relative energy band alignment and the charge-transfer
efficiency are locked. Due to their large variety and broad size tunability,
semiconductor quantum dots (0D-QDs) interfaced with 2D-TMDs may become
an attractive heterostructure for optoelectronic applications. Here,
we incorporate femtosecond pump–probe spectroscopy to reveal
the sub-45 fs charge transfer at a 2D/0D heterostructure composed
of tungsten disulfide monolayers (2D-WS<sub>2</sub>) and a single
layer of cadmium selenide/zinc sulfide core/shell 0D-QDs. Furthermore,
ultrafast dynamics and steady-state measurements suggested that, following
electron transfer from the 2D to the 0D, hybrid excitons, wherein
the electron resides in the 0D and the hole resides in the 2D-TMD
monolayer, are formed with a binding energy on the order of ∼140
meV, which is several times lower than that of tightly bound excitons
in 2D-TMDs
Ultrafast Dynamics of Metal Plasmons Induced by 2D Semiconductor Excitons in Hybrid Nanostructure Arrays
With the advanced
progress achieved in the field of nanotechnology,
localized surface plasmon resonances are actively considered to improve
the efficiency of metal-based photocatalysis, photodetection, and
photovoltaics. Here, we report on the exchange of energy and electric
charges in a hybrid composed of a two-dimensional tungsten disulfide
(2D-WS<sub>2</sub>) monolayer and an array of aluminum (Al) nanodisks.
Femtosecond pump–probe spectroscopy results indicate that within
∼830 fs after photoexcitation of the 2D-WS<sub>2</sub> semiconductor
energy transfer from the 2D-WS<sub>2</sub> excitons excites the plasmons
of the Al array. Then, upon the radiative and/or nonradiative damping
of these excited plasmons, energy and/or electron transfer back to
the 2D-WS<sub>2</sub> semiconductor takes place as indicated by an
increase in the reflected probe at the 2D-exciton transition energies
at later time delays. This simultaneous exchange of energy and charges
between the metal and the 2D-WS<sub>2</sub> semiconductor resulted
in an extension of the average lifetime of the 2D-excitons from ∼15
ps to ∼58 ps in the absence and presence of the Al array, respectively.
Furthermore, the indirectly excited plasmons were found to live as
long as the 2D-WS<sub>2</sub> excitons exist. The demonstrated ability
to generate exciton–plasmon coupling in a hybrid nanostructure
may open new opportunities for optoelectronic applications such as
plasmonic-based photodetection and photocatalysis
Interlayer Coupling in Twisted WSe<sub>2</sub>/WS<sub>2</sub> Bilayer Heterostructures Revealed by Optical Spectroscopy
van
der Waals (vdW) heterostructures are promising building blocks
for future ultrathin electronics. Fabricating vdW heterostructures
by stamping monolayers at arbitrary angles provides an additional
range of flexibility to tailor the resulting properties than could
be expected by direct growth. Here, we report fabrication and comprehensive
characterizations of WSe<sub>2</sub>/WS<sub>2</sub> bilayer heterojunctions
with various twist angles that were synthesized by artificially stacking
monolayers of WS<sub>2</sub> and WSe<sub>2</sub> grown by chemical
vapor deposition. After annealing the WSe<sub>2</sub>/WS<sub>2</sub> bilayers, Raman spectroscopy reveals interlayer coupling with the
appearance of a mode at 309.4 cm<sup>–1</sup> that is sensitive
to the number of WSe<sub>2</sub> layers. This interlayer coupling
is associated with substantial quenching of the intralayer photoluminescence.
In addition, microabsorption spectroscopy of WSe<sub>2</sub>/WS<sub>2</sub> bilayers revealed spectral broadening and shifts as well
as a net ∼10% enhancement in integrated absorption strength
across the visible spectrum with respect to the sum of the individual
monolayer spectra. The observed broadening of the WSe<sub>2</sub> A
exciton absorption band in the bilayers suggests fast charge separation
between the layers, which was supported by direct femtosecond pump–probe
spectroscopy. Density functional calculations of the band structures
of the bilayers at different twist angles and interlayer distances
found robust type II heterojunctions at all twist angles, and predicted
variations in band gap for particular atomistic arrangements. Although
interlayer excitons were indicated using femtosecond pump–probe
spectroscopy, photoluminescence and absorption spectroscopies did
not show any evidence of them, suggesting that the interlayer exciton
transition is very weak. However, the interlayer coupling for the
WSe<sub>2</sub>/WS<sub>2</sub> bilayer heterojunctions indicated by
substantial PL quenching, enhanced absorption, and rapid charge transfer
was found to be insensitive to the relative twist angle, indicating
that stamping provides a robust approach to realize reliable optoelectronics
CdSe Quantum Dot–Fullerene Hybrid Nanocomposite for Solar Energy Conversion: Electron Transfer and Photoelectrochemistry
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