5 research outputs found
Quantum Dots-Facilitated Printing of ZnO Nanostructure Photodetectors with Improved Performance
A nanocomposite
ink composed of zinc oxide precursor (ZnOPr) and
crystalline ZnO quantum dots (ZnOPrQDs) has been explored for printing
high-performance ultraviolet (UV) photodetectors. The performance
of the devices has been compared with their counterparts’ printed
from ZnOPr ink without ZnO QDs. Remarkably, higher UV photoresponsivity
of 383.6 A/W and the on/off ratio of 2470 are observed in the former,
which are significantly better than 14.7 A/W and 949 in the latter.
The improved performance is attributed to the increased viscosity
in the nanocomposite ink to enable a nanoporous structure with improved
crystallinity and surface-to-volume ratio. This is key to enhanced
surface electron-depletion effect for higher UV responsivity and on/off
ratio. In addition, the QD-assisted printing provides a simple and
robust method for printing high-performance optoelectronics and sensors
Printable Nanocomposite FeS<sub>2</sub>–PbS Nanocrystals/Graphene Heterojunction Photodetectors for Broadband Photodetection
Colloidal nanocrystals are attractive
materials for optoelectronics
applications because they offer a compelling combination of low-cost
solution processing, printability, and spectral tunability through
the quantum dot size effect. Here we explore a novel nanocomposite
photosensitizer consisting of colloidal nanocrystals of FeS<sub>2</sub> and PbS with complementary optical and microstructural properties
for broadband photodetection. Using a newly developed ligand exchange
to achieve high-efficiency charge transfer across the nanocomposite
FeS<sub>2</sub>–PbS sensitizer and graphene on the FeS<sub>2</sub>–PbS/graphene photoconductors, an extraordinary photoresponsivity
in exceeding ∼10<sup>6</sup> A/W was obtained in an ultrabroad
spectrum of ultraviolet (UV)-visible-near-infrared (NIR). This is
in contrast to the nearly 3 orders of magnitude reduction of the photoresponsivity
from ∼10<sup>6</sup> A/W at UV to 10<sup>3</sup> A/W at NIR
on their counterpart of FeS<sub>2</sub>/graphene detectors. This illustrates
the combined advantages of the nanocomposite sensitizers and the high
charge mobility in FeS<sub>2</sub>–PbS/graphene van der Waals
heterostructures for nanohybrid optoelectronics with high performance,
low cost, and scalability for commercialization
Heat-Assisted Inkjet Printing of Tungsten Oxide for High-Performance Ultraviolet Photodetectors
An ammonium metatungstate
precursor (WO<sub>3</sub>Pr) ink was printed for tungsten oxide (WO<sub>3</sub>) UV detectors on SiO<sub>2</sub>/Si wafers with prefabricated
Au electrodes. A systematic study was carried out on the printing
parameters including substrate temperatures in the range of 22–80
°C, WO<sub>3</sub>Pr molar concentrations of 0.01, 0.02, and
0.03 M, and printing scan numbers up to 7 to understand their effects
on the resulted WO<sub>3</sub> film morphology and optoelectronic
properties. It has been found that the printing parameters can sensitively
affect the WO<sub>3</sub> film morphology, which in turn impacts the
WO<sub>3</sub> photodetector performance. In particular, the printed
films experienced a systematic change from discontinuous droplets
at below 40 °C to continuous films at 40–60 °C of
the substrate temperature. At higher temperatures, the excessive heat
from the substrate not only caused drastic evaporation of the printed
ink, resulting in highly nonuniform films, but also detrimental heating
of the ink in the printer nozzle in proximity of the substrate, preventing
continuous printing operation. An optimal printing window of the substrate
temperature of 45–55 °C at a molar concentration of 0.02
M of ammonium metatungstate and three printing scans was obtained
for the best UV detector performance. A large on/off ratio of 3538
and a high responsivity up to 2.70 A/W at 5 V bias (0.54 A/W·V)
represent a significant improvement over the best report of ∼0.28
μA/W·V on WO<sub><i>X</i></sub> photodetectors,
which indicates that the printed WO<sub>3</sub> films are promising
for various applications of optoelectronics and sensors
Interface Nanojunction Engineering of Electron-Depleted Tungsten Oxide Nanoparticles for High-Performance Ultraviolet Photodetection
This
work reports a general and facile route, i.e., thermal decomposition
of a precursor followed by ultrafast thermal annealing (TDP-UTA),
to the in situ fabrication of a nanojunction-interlinked tungsten
oxide nanoparticle (WO<sub>3</sub>-NP) networks for extraordinary
ultraviolet (UV) photodetection. TDP leads a spin-coated ammonium
metatungstate thin layer to in situ self-assemble into a highly crystalline
WO<sub>3</sub>-NP mesoporous film on SiO<sub>2</sub>/Si substrates
with prepatterned electrodes. The as-synthesized WO<sub>3</sub>-NPs
have dimensions comparable to the Debye length (≈43 nm), which
is critical to the optimal electron-depletion effect for high gain
in photodetection. UTA creates the NP–NP interface nanojunctions
between neighboring WO<sub>3</sub>-NPs, which is the key to high-efficiency
electron transport with minimized charge recombination in optoelectronic
processes. The photodetectors based on such nanojunction-interlinked
WO<sub>3</sub>-NP networks exhibit a photocurrent-to-dark-current
ratio of 5600, the highest value for any WO<sub><i>x</i></sub>-based photodetectors ever reported. Moreover, the obtained
photoresponsivity is up to 139 A/W (or 27.8 A/W·V) upon 360 nm
illumination, which is over 1 order of magnitude higher than that
of any previously reported WO<sub><i>x</i></sub>-nanostructure
film photodetectors. These results demonstrate that the TDP-UTA route
is a low-cost, robust, and scalable pathway to the in situ fabrication
of interlinked semiconducting-nanostructure networks for high-performance
optoelectronics and sensors