7 research outputs found
Z‑scheme Photocatalytic CO<sub>2</sub> Conversion on Three-Dimensional BiVO<sub>4</sub>/Carbon-Coated Cu<sub>2</sub>O Nanowire Arrays under Visible Light
Cuprous
oxide (Cu<sub>2</sub>O) is one of the most promising materials
for photoreduction of CO<sub>2</sub> because of its high conduction
band and small band gap, which enable the production of high-potential
electrons under visible-light irradiation. However, it is difficult
to reduce the CO<sub>2</sub> using a Cu<sub>2</sub>O-based photocatalyst
due to fast charge recombination and low photostability. In this work,
we enhanced the photocatalytic CO<sub>2</sub> conversion activity
of Cu<sub>2</sub>O by hybridization of Cu<sub>2</sub>O NWAs, carbon
layers, and BiVO<sub>4</sub> nanoparticles. By construction of a Z-scheme
charge flow on a 3-D NWA structure, the BiVO<sub>4</sub>/carbon-coated
Cu<sub>2</sub>O (BVO/C/Cu<sub>2</sub>O) NWAs show significantly enhanced
charge separation and light harvesting property. As a result, CO formation
rate of BVO/C/Cu<sub>2</sub>O was 9.4 and 4.7 times those of Cu<sub>2</sub>O mesh and Cu<sub>2</sub>O NWAs, respectively, under visible
light irradiation. In addition, the material retained 98% of its initial
photocatalytic CO<sub>2</sub> conversion performance after five reaction
cycles (20 h) because of the protective carbon layer and Z-schematic
charge flow. We believe that this work provides a promising photocatalyst
system that combines a 3-D NWA structure and a Z-scheme charge flow
for efficient and stable CO<sub>2</sub> conversion
Improving Uniformity and Reproducibility of Hybrid Perovskite Solar Cells via a Low-Temperature Vacuum Deposition Process for NiO<i><sub>x</sub></i> Hole Transport Layers
Recently,
the trend in inverted hybrid perovskite solar cells (PVSCs) has been
to utilize NiO<i><sub>x</sub></i> as hole transport layers.
However, the majority of reported solution-processed NiO<i><sub>x</sub></i> films require a high-temperature thermal annealing
process, which is unfavorable for large-scale manufacturing and suffers
from lack of uniformity. We report, for the first time, e-beam evaporation
as a low-temperature vacuum process for the deposition of NiO<i><sub>x</sub></i> hole transport layers for PVSCs. Device characterization
shows that efficiency is on par with solution-processed methods, the
highest efficiency at 15.4% with no obvious hysteresis. Differences
are found to be due to the presence of more Ni<sup>3+</sup> in e-beam
evaporated NiO<i><sub>x</sub></i>, which are responsible
for a lower transmittance but higher conductivity. Most importantly,
e-beam-evaporated NiO<i><sub>x</sub></i>-based PVSCs show
greater uniformity and reproducibility compared to spin-coated NiO<i><sub>x</sub></i>-based PVSCs. Finally, e-beam-evaporated NiO<i><sub>x</sub></i> has the additional advantage of being produced
by a low-temperature deposition process and applicable over large
areas. This work, therefore, represents a significant step toward
large-area PVSCs, where e-beam evaporation can be used for the low-temperature
uniform deposition of charge-transport layers, such as NiO<i><sub>x</sub></i>
Highly Transparent and UV-Resistant Superhydrophobic SiO<sub>2</sub>‑Coated ZnO Nanorod Arrays
Highly transparent and UV-resistant superhydrophobic arrays of SiO<sub>2</sub>-coated ZnO nanorods are prepared in a sequence of low-temperature (<150 °C) steps on both glass and thin sheets of PET (2 × 2 in.<sup>2</sup>), and the superhydrophobic nanocomposite is shown to have minimal impact on solar cell device performance under AM1.5G illumination. Flexible plastics can serve as front cell and backing materials in the manufacture of flexible displays and solar cells
Highly Efficient and Stable CO<sub>2</sub> Reduction Photocatalyst with a Hierarchical Structure of Mesoporous TiO<sub>2</sub> on 3D Graphene with Few-Layered MoS<sub>2</sub>
The development of photocatalysts of CO<sub>2</sub> reduction based
on stable and Earth-abundant materials is essential for utilizing
solar energy and storing it in chemical forms. Here, we report the
synthesis and characterization of a composite material consisting
of a few layers of MoS<sub>2</sub> on a hierarchical porous structure
of mesoporous TiO<sub>2</sub> and macroporous 3D graphene aerogel
(TGM) as a high-performance, robust, noble-metal-free photocatalyst
of CO<sub>2</sub> reduction. The hierarchical structure contributed
to the high photocatalytic catalyst performance, which was investigated
by controlling the morphologies of the mesopores and macropores. By
optimizing the relative amounts of each component and the configuration
of the composite, a TGM system was fabricated. The resulting TGM showed
a lower extent of charge recombination and a higher photocurrent density,
and hence a higher CO photoconversion rate (92.33 μmol CO/g·h)
than those of other composite combinations, i.e., bare TiO<sub>2</sub>, TiO<sub>2</sub>-graphene, TiO<sub>2</sub>-MoS<sub>2</sub>, and
TiO<sub>2</sub>-graphene multiple-layered MoS<sub>2</sub>. Also, the
role of each component and the underlying mechanism in the catalysis
of the reaction by TGM were investigated. The long-term stability
of the TGM composite was tested and compared with that of a TiO<sub>2</sub>-graphene-Ag composite. Over the course of 15 cycles, the
TGM composite retained its original conversion rate, while the activity
of the TiO<sub>2</sub>-graphene-Ag composite decreased. The hierarchical
porous structure with mesoporous TiO<sub>2</sub> and a few layers
of MoS<sub>2</sub> on macroporous 3D graphene is expected to have
great potential as an affordable, robust, high-efficiency CO-selective
photocatalyst of CO<sub>2</sub> reduction
Amine-Functionalized Graphene/CdS Composite for Photocatalytic Reduction of CO<sub>2</sub>
This
study provides a significant enhancement in CO<sub>2</sub> photoconversion
efficiency by the functionalization of a reduced
graphene oxide/cadmium sulfide composite (rGO/CdS) with amine. The
amine-functionalized graphene/CdS composite (AG/CdS) was obtained
in two steps. First, graphene oxide (GO) was selectively deposited
via electrostatic interaction with CdS nanoparticles modified with
3-aminopropyltriethoxysilane. Subsequently, ethylenediamine (NH<sub>2</sub>C<sub>2</sub>H<sub>4</sub>NH<sub>2</sub>) was grafted by an <i>N</i>,<i>N</i>′-dicyclohexylcarbodiimide coupling
reaction between the amine group of ethylenediamine and the carboxylic
group of GO. As a result, a few layers of amine-functionalized graphene
wrapped CdS uniformly, forming a large interfacial area. Under visible
light, the photocurrent through the AG/CdS significantly increased
because of enhanced charge separation in CdS. The CO<sub>2</sub> adsorption
capacity on AG/CdS was 4 times greater than that on rGO/CdS at 1 bar.
These effects resulted in a methane formation rate of 2.84 μmol/(g
h) under visible light and CO<sub>2</sub> at 1 bar, corresponding
to 3.5 times that observed for rGO/CdS. Interestingly, a high methane
formation rate (1.62 μmol/(g h)) was observed for AG/CdS under
CO<sub>2</sub> at low pressure (0.1 bar), corresponding to a value
20 times greater than that observed for the rGO/CdS. Thus, the enhanced
performance for photocatalytic reduction of CO<sub>2</sub> on the
AG/CdS is due to the improved CO<sub>2</sub> adsorption related to
the amine groups on amine-functionalized graphene, which sustains
the strong absorption of visible light and superior charge-transfer
properties in comparison with those of graphene
Ultralong Radiative States in Hybrid Perovskite Crystals: Compositions for Submillimeter Diffusion Lengths
Organic–inorganic
hybrid perovskite materials have recently
evolved into the leading candidate solution-processed semiconductor
for solar cells due to their combination of desirable optical and
charge transport properties. Chief among these properties is the long
carrier diffusion length, which is essential to optimizing the device
architecture and performance. Herein, we used time-resolved photoluminescence
(at low excitation fluence, 10.59 μJ·cm<sup>–2</sup> upon two-photon excitation), which is the most accurate and direct
approach to measure the radiative charge carrier lifetime and diffusion
lengths. Lifetimes of about 72 and 4.3 μs for FAPbBr<sub>3</sub> and FAPbI<sub>3</sub> perovskite single crystals have been recorded,
presenting the longest radiative carrier lifetimes reported to date
for perovskite materials. Subsequently, carrier diffusion lengths
of 107.2 and 19.7 μm are obtained. In addition, we demonstrate
the key role of the organic cation units in modulating the carrier
lifetime and its diffusion lengths, in which the defect formation
energies for FA cations are much higher than those with the MA ones
Inside Perovskites: Quantum Luminescence from Bulk Cs<sub>4</sub>PbBr<sub>6</sub> Single Crystals
Zero-dimensional
perovskite-related structures (0D-PRS) are a new
frontier of perovskite-based materials. 0D-PRS, commonly synthesized
in powder form, manifest distinctive optical properties such as strong
photoluminescence (PL), narrow emission line width, and high exciton
binding energy. These properties make 0D-PRS compelling for several
types of optoelectronic applications, including phosphor screens and
electroluminescent devices. However, it would not be possible to rationally
design the chemistry and structure of these materials, without revealing
the origins of their optical behavior, which is contradictory to the
well-studied APbX<sub>3</sub> perovskites. In this work, we synthesize
single crystals of Cs<sub>4</sub>PbBr<sub>6</sub> 0D-PRS, and investigated
the origins of their unique optical and electronic properties. The
crystals exhibit a PL quantum yield higher than 40%, the highest reported
for perovskite-based single crystals. Time-resolved and temperature
dependent PL studies, supported by DFT calculations, and structural
analysis, elucidate an emissive behavior reminiscent of a quantum
confined structure rather than a typical bulk perovskite material