23 research outputs found
One-Pot Noninjection Synthesis of Cu-Doped Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S Nanocrystals with Emission Color Tunable over Entire Visible Spectrum
Unlike Mn doped quantum dots (d-dots), the emission color
of Cu
dopant in Cu d-dots is dependent on the nature, size, and composition
of host nanocrystals (NCs). The tunable Cu dopant emission has been
achieved via tuning the particle size of host NCs in previous reports.
In this paper, for the first time we doped Cu impurity in Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S alloyed
NCs and tuned the dopant emission in the whole visible spectrum via
variation of the stoichiometric ratio of Zn/Cd precursors in the host
Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S alloyed NCs. A facile noninjection and low cost approach for the
synthesis of Cu:Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S d-dots was reported. The optical properties and
structure of the obtained Cu:Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S d-dots have been characterized
by UV–vis spectroscopy, photoluminescence (PL) spectroscopy,
transmission electron microscopy (TEM), and X-ray diffraction (XRD).
The influences of various experimental variables, including Zn/Cd
ratio, reaction temperature, and Cu dopant concentration, on the optical
properties of Cu dopant emission have been systematically investigated.
The as-prepared Cu:Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S d-dots did show PL emission but with quite low
quantum yield (QY) (typically below 6%). With the deposition of ZnS
shell around the Cu:Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S core NCs, the PL QY increased substantially with
a maximum value of 65%. More importantly, the high PL QY can be preserved
when the initial oil-soluble d-dots were transferred into aqueous
media via ligand replacement by mercaptoundeconic acid. In addition,
these d-dots have thermal stability up to 250 °C
Noninjection Facile Synthesis of Gram-Scale Highly Luminescent CdSe Multipod Nanocrystals
Nearly all reported approaches for synthesis of high
quality CdSe
nanocrystals (NCs) involved two steps of preparation of Cd or Se stock
solution in advance and then mixing the two reactants via hot-injection
in high temperature. In this manuscript, Gram-scale CdSe multipod
NCs were facilely synthesized in a noninjection route with the use
of CdO and Se powder directly as reactants in paraffin reaction medium
containing small amount of oleic acid and trioctylphosphine. The influence
of various experimental variables, including reaction temperature,
nature and amount of surfactants, Cd-to-Se ratio, and the nature of
reactants, on the morphology of the obtained CdSe NCs have been systematically
investigated. After deposition of ZnS shell around the CdSe multipod
NCs, the PL QY of the obtained CdSe/ZnS can be up to 85%. The reported
noninjection preparation approach can satisfy the requirement of industrial
production bearing the advantage of low-cost, reproducible, and scalable.
Furthermore, this facile noninjection strategy provides a versatile
route to large-scale preparation of other semiconductor NCs with multipod
or other morphologies
Electroplating Cuprous Sulfide Counter Electrode for High-Efficiency Long-Term Stability Quantum Dot Sensitized Solar Cells
Currently,
Cu<sub>2</sub>S based on brass foil is the most commonly used counter
electrode (CE) in high efficiency quantum dot sensitized solar cells
(QDSCs) because of its superior catalytic activity to the polysulfide
electrolyte redox couple. Regretfully, the brass substrate is limited
by the shortcomings of corrosion by polysulfide electrolyte and lack
of long-term stability. In order to combine the high catalytic activity
of Cu<sub>2</sub>S and superior tolerance of fluorine doped tin oxide
(FTO) glass to polysulfide electrolyte, Cu<sub>2</sub>S film on the
FTO glass substrate (Cu<sub>2</sub>S/FTO) CE was prepared by electrodeposition
of the copper film via a multipotential step technique followed by
dipping into polysulfide methanol solution. The Cu<sub>2</sub>S film
was proven to be composed by the interconnected nanoflakes, which
ensures the highly catalytic activity to the polysulfide redox couple
electrolyte in QDSCs. The CdSe quantum dot (QD) sensitized solar cells
with the optimized Cu<sub>2</sub>S/FTO CE exhibit a power conversion
efficiency (PCE) of 5.21%, which is very close to that with the commonly
used Cu<sub>2</sub>S/brass CE (5.41%) and much higher than that of
Pt CE (1.68%). Furthermore, the cell device based on the Cu<sub>2</sub>S/FTO CE shows superior stability at a working state for over 10
h without decrease in PCE, which is a serious challenge for the Cu<sub>2</sub>S/brass CE
Inorganic Ligand Thiosulfate-Capped Quantum Dots for Efficient Quantum Dot Sensitized Solar Cells
The
insulating nature of organic ligands containing long hydrocarbon tails
brings forward serious limitations for presynthesized quantum dots
(QDs) in photovoltaic applications. Replacing the initial organic
hydrocarbon chain ligands with simple, cheap, and small inorganic
ligands is regarded as an efficient strategy for improving the performance
of the resulting photovoltaic devices. Herein, thiosulfate (S<sub>2</sub>O<sub>3</sub><sup>2–</sup>), and sulfide (S<sup>2–</sup>) were employed as ligand-exchange reagents to get access to the
inorganic ligand S<sub>2</sub>O<sub>3</sub><sup>2–</sup>- and
S<sup>2–</sup>-capped CdSe QDs. The obtained inorganic ligand-capped
QDs, together with the initial oleylamine-capped QDs, were used as
light-absorbing materials in the construction of quantum dot sensitized
solar cells (QDSCs). Photovoltaic results indicate that thiosulfate-capped
QDs give excellent power conversion efficiency (PCE) of 6.11% under
the illumination of full one sun, which is remarkably higher than
those of sulfide- (3.36%) and OAm-capped QDs (0.84%) and is comparable
to the state-of-the-art value based on mercaptocarboxylic acid capped
QDs. Photoluminescence (PL) decay characterization demonstrates that
thiosulfate-based QDSCs have a much-faster electron injection rate
from QD to TiO<sub>2</sub> substrate in comparison with those of sulfide-
and OAm-based QDSCs. Electrochemical impedance spectroscopy (EIS)
results indicate that higher charge-recombination resistance between
potoanode and eletrolyte interfaces were observed in the thiosulfate-based
cells. To the best of our knowledge, this is the first application
of thiosulfate-capped QDs in the fabrication of efficient QDSCs. This
will lend a new perspective to boosting the performance of QDSCs furthermore
Controlled Sulfidation Approach for Copper Sulfide–Carbon Hybrid as an Effective Counter Electrode in Quantum-Dot-Sensitized Solar Cells
Because of their good conductivities
and high catalytic activities,
carbon materials and copper sulfides have been individually and jointly
used as counter electrodes in quantum-dot-sensitized solar cells (QDSCs).
However, obtaining a combination of high conversion efficiency and
stability is still challenging. In this work, we present a facile
method for fabricating Cu<sub>1.8</sub>S–C hybrid counter electrodes
through the sulfidation of a copper–carbon composite synthesized
by grinding a mixture of organic binder, commercial copper powder,
and carbon material containing activated carbon and carbon black in
a designed mass ratio. The assembled CdSeTe-sensitized QDSCs achieved
a high PCE of 8.40%, larger than that of pure carbon (5.25%) and comparable
to that of conventional Cu<sub><i>x</i></sub>S/brass-based
QDSCs (8.44%). Significantly, the devices based on Cu<sub>1.8</sub>S–C showed excellent stability. The improved performance is
mainly attributed to the good conductivity and stability of carbon
and the high catalytic activity of Cu<sub>1.8</sub>S
Solar Paint from TiO<sub>2</sub> Particles Supported Quantum Dots for Photoanodes in Quantum Dot–Sensitized Solar Cells
The preparation of
quantum dot (QD)–sensitized photoanodes,
especially the deposition of QDs on TiO<sub>2</sub> matrix, is usually
a time-extensive and performance-determinant step in the construction
of QD-sensitized solar cells (QDSCs). Herein, a transformative approach
for immobilizing QD on the TiO<sub>2</sub> matrix was developed by
simply mixing the as-prepared oil-soluble QDs with TiO<sub>2</sub> P25 particles suspension for a period as short as half a minute.
The solar paint was prepared by adding the TiO<sub>2</sub>/QD composite
in a binder solution under ultrasonication. The QD-sensitized photoanodes
were then obtained by simply brushing the solar paint on a fluorine-doped
tin oxide substrate followed by a low-temperature annealing at ambient
atmosphere. Sandwich-structured complete QDSCs were assembled with
the use of Cu<sub>2</sub>S/brass as counter electrode and polysulfide
redox couple as an electrolyte. The photovoltaic performance of the
resulting Zn–Cu–In–Se (ZCISe) QDSCs was evaluated
after primary optimization of the QD/TiO<sub>2</sub> ratio as well
as the thicknesses of photoanode films. In this proof of concept with
a simple solar paint approach for photoanode films, an average power
conversion efficiency of 4.13% (<i>J</i><sub>sc</sub> =
11.11 mA/cm<sup>2</sup>, <i>V</i><sub>oc</sub> = 0.590 V,
fill factor = 0.631) was obtained under standard irradiation condition.
This facile solar paint approach offers a simple and convenient approach
for QD-sensitized photoanodes in the construction of QDSCs
Color-Tunable Highly Bright Photoluminescence of Cadmium-Free Cu-Doped Zn–In–S Nanocrystals and Electroluminescence
A series of Cu doped
Zn–In–S quantum dots (Cu:Zn–In–S
d-dots) were synthesized via a one-pot noninjection synthetic approach
by heating up a mixture of corresponding metal acetate salts and sulfur
powder together with dodecanethiol in oleylamine media. After overcoating
the ZnS shell around the Cu:Zn–In–S d-dot cores directly
in the crude reaction solution, the resulting Cu:Zn–In–S/ZnS
d-dots show composition-tunable photoluminescence (PL) emission over
the entire visible spectral window and extending to the near-infrared
spectral window (from 450 to 810 nm), with the highest PL quantum
yield (QY) up to 85%. Importantly, the initial high PL QY of the obtained
Cu:Zn–In–S/ZnS d-dots in organic media can be preserved
when transferred into aqueous media via ligand exchange. Furthermore,
electroluminescent devices with good performance (with a maximum luminance
of 220 cd m<sup>–2</sup>, low turn-on voltages of 3.6 V) have
been fabricated with the use of these Cd-free low toxicity yellow-emission
Cu:Zn–In–S/ZnS d-dots as an active layer in these QD-based
light-emitting diodes
Highly Efficient Inverted Type-I CdS/CdSe Core/Shell Structure QD-Sensitized Solar Cells
Presynthesized high-quality CdS/CdSe inverted type-I core/shell structure QDs have been deposited onto TiO<sub>2</sub> electrodes after first coating with bifunctional linker molecules, mercaptopropionic acid (MPA), and the resulting quantum dot sensitized solar cells (QDSCs) exhibited record conversion efficiency of 5.32% (<i>V</i><sub>oc</sub> = 0.527 V, <i>J</i><sub>sc</sub> = 18.02 mA/cm<sup>2</sup>, FF = 0.56) under simulated AM 1.5, 100 mW cm<sup>–2</sup> illumination. CdS/CdSe QDs with different CdSe shell thicknesses and different corresponding absorption onsets were prepared <i>via</i> the well-developed organometallic high-temperature injection method. MPA-capped water-dispersible QDs were then obtained <i>via</i> ligand exchange from the initial organic ligand capped oil-dispersible QDs. The QD-sensitized TiO<sub>2</sub> electrodes were facilely prepared by pipetting the MPA-capped CdS/CdSe QD aqueous solution onto the TiO<sub>2</sub> film, followed by a covering process with a ZnS layer and a postsintering process at 300 °C. Polysulfide electrolyte and Cu<sub>2</sub>S counterelectrode were used to provide higher photocurrents and fill factors of the constructed cell devices. The characteristics of these QDSCs were studied in more detail by optical measurements, incidental photo-to-current efficiency measurements, and impedance spectroscopy. With the combination of the modified deposition technique with use of linker molecule MPA-capped water-soluble QDs and well-developed inverted type-I core/shell structure of the sensitizer together with the sintering treatment of QD-bound TiO<sub>2</sub> electrodes, the resulting CdS/CdSe-sensitized solar cells show a record photovoltaic performance with a conversion efficiency of 5.32%
Topotactically Grown Bismuth Sulfide Network Film on Substrate as Low-Cost Counter Electrodes for Quantum Dot-Sensitized Solar Cells
Bi<sub>2</sub>S<sub>3</sub> films
consisting of two-dimensional
interconnected Bi<sub>2</sub>S<sub>3</sub> single-crystalline nanorod
networks have been fabricated on a F:SnO<sub>2</sub> (FTO) glass substrate
through the formation of intermediate BiOI nanosheets from layer-structured
BiI<sub>3</sub> by chemical vapor deposition and subsequent hydrothermal
transformation into Bi<sub>2</sub>S<sub>3</sub> networks. A continuous
lattice and structure-directed topotactic transformation mechanism
is supposed for the formation of Bi<sub>2</sub>S<sub>3</sub> network
film. The prepared Bi<sub>2</sub>S<sub>3</sub>/FTO films were employed
as counter electrode (CE) for CdSe quantum dot-sensitized solar cells
for the first time and showed better photovoltaic performance than
that from the convenient Pt CE. The influence of the preparation conditions
for Bi<sub>2</sub>S<sub>3</sub>/FTO films on the resulting solar cell
performance was systematically investigated and optimized with use
of <i>J–V</i> curves, scanning electron microscopy
(SEM), UV–vis absorption, and electrochemical impedance spectroscopy.
To further improve the cell device efficiency, the modification of
the Bi<sub>2</sub>S<sub>3</sub> network CE with metal particles was
also studied
Effects of Metal Oxyhydroxide Coatings on Photoanode in Quantum Dot Sensitized Solar Cells
Exploring facile modifications on
photoanode to suppress charge
recombination at photoanode/electrolyte interfaces is an efficient
way to improve the performance of quantum dot sensitized solar cells
(QDSCs). Herein, a series of metal oxyhydroxide gels have been overcoated
on CdSeTe QD sensitized photoanodes via a hydrolysis and condensation
process from the corresponding metal chloride (NbCl<sub>5</sub>, ZrOCl<sub>2</sub>, SnCl<sub>4</sub>, FeCl<sub>3</sub>, AlCl<sub>3</sub>, CoCl<sub>2</sub>, CuCl<sub>2</sub>, MgCl<sub>2</sub>, and ZnCl<sub>2</sub>) aqueous solutions, and their effects on the photovoltaic performance
are systematically investigated. Photovoltaic measurement results
indicate that the NbCl<sub>5</sub> and ZrOCl<sub>2</sub> modifications
offer a remarkable enhancement in photovoltaic performance, especially
in photovoltage. The SnCl<sub>4</sub> AlCl<sub>3</sub>, MgCl<sub>2</sub>, and ZnCl<sub>2</sub> treatments give a negligible influence, and
the FeCl<sub>3</sub>, CuCl<sub>2</sub>, and CoCl<sub>2</sub> treatments
present a negative effect on the performance. DFT calculations suggest
that different metal oxyhydroxide coatings bring forward distinct
densities of empty states at the surface of TiO<sub>2</sub>, which
correspond to different charge recombination kinetics and therefore
different photovoltaic performance. Electrochemical impedance spectroscopy
(EIS) and open-circuit voltage decay (OCVD) measurements confirm further
the suppressed charge recombination process after coating with the
amorphous Zr or Nb oxyhydroxide layer. In all, an impressive power
conversion efficiency (PCE) of 9.73% (<i>J</i><sub>sc</sub> = 21.04 mA/cm<sup>2</sup>, <i>V</i><sub>oc</sub> = 0.720
V, FF = 0.642) was obtained for CdSeTe-based QDSCs with ZrOCl<sub>2</sub> modification on photoanode