5 research outputs found
Improved Electrical Transport and Electroluminescence Properties of p‑ZnO/n-Si Heterojunction via Introduction of Patterned SiO<sub>2</sub> Intermediate Layer
The authors report on the fabrication
and temperature-dependent current–voltage and electroluminescence
properties of p-ZnO:As/n-Si heterojunction diodes. The As-doped p-ZnO
material was prepared by out-diffusion of arsenic atoms from a sandwiched
GaAs interlayer on patterned SiO<sub>2</sub>/Si substrates. The introduction
of hollow-shaped SiO<sub>2</sub> patterned layer promotes the efficiency
of carrier injection into the active layer and considerably lowers
the emission onset of the studied diode. The current–voltage
characteristics of the heterojunction were detailedly studied in the
temperature range of 21–120 °C to determine the dominant
carrier transport mechanisms in different bias regions. The reverse
saturation current, barrier height, and ideality factor were estimated
from the thermionic emission model and found to be highly temperature
dependent. An improved electroluminescence performance of the studied
diode featuring an ultralow emission onset and an acceptable operation
stability shows the potential of our approach. Long-term stability
of the diode without encapsulation in air-exposure environment was
also investigated by monitoring the electroluminescence evolution
with storage time, and the oxygen-related surface adsorption was identified
as the main cause for the undesirable emission decay
High-Efficiency and Air-Stable Perovskite Quantum Dots Light-Emitting Diodes with an All-Inorganic Heterostructure
Perovskite
light-emitting diodes (PeLEDs), because of its fundamental scientific
importance and practical applications in the fields of low-cost light
source or display applications, have drawn worldwide attention in
recent years. However, PeLEDs available today suffer from a compromise
in their emission efficiency and operation stability. In this study,
we designed and fabricated a stacking all-inorganic multilayer structure
by using inorganic perovskite CsPbBr<sub>3</sub> quantum dots (QDs)
as the emissive layer and inorganic n-type MgZnO and p-type MgNiO
as the carrier injectors, respectively. Through energy band engineering
of carrier injectors by Mg incorporation and their thickness optimization,
PeLEDs with maximum luminance of 3809 cd/m<sup>2</sup>, luminous efficiency
of 2.25 cd/A, and external quantum efficiency of 2.39% have been realized,
which are much better than most PeLEDs from CH<sub>3</sub>NH<sub>3</sub>PbBr<sub>3</sub> films, and comparable with the highest results reported
on CsPbBr<sub>3</sub> QDs LEDs. More importantly, the unencapsulated
PeLEDs in a continuous current mode demonstrate a remarkable operation
stability against water and oxygen degradation. After a continuous
operation for 10 h under a dc bias (10.0 V), nearly 80% of the original
efficiency of the PeLEDs has been retained, greatly superior to reference
and other previously reported devices constructed with conventional
organic carrier injectors. Our results obtained open possibilities
for the design and development of high-efficiency and air-stable PeLEDs
that are not dependent on expensive and less-stable organic carrier
injectors
Controllable Vapor-Phase Growth of Inorganic Perovskite Microwire Networks for High-Efficiency and Temperature-Stable Photodetectors
Recently,
metal halide perovskites have attracted tremendous research
interest due to their exceptional optoelectronic properties, showing
great application potentials in the fields of solar cells, light-emitting
diodes, and photodetectors. However, most of the previously reported
perovskite photodetectors are based on the polycrystalline perovskite
films, and the amounts of defects and large grain boundaries in the
films are unfavorable for further improvement of the performance of
the device. In this study, high-quality CsPbCl<sub>3</sub> microwire
networks (MWNs) were successfully prepared by a vapor-phase method.
By changing the evaporation temperature of source powders, a series
of MWs with different widths and coverage can be obtained. Ag electrodes
were thermally deposited onto the surface of the mica substrate through
a shadow mask, and symmetrically structured photoconductive detectors
were fabricated. The performance of the studied photodetector is remarkable
in terms of its high on/off photocurrent ratio of 2.0 Ă— 10<sup>3</sup>, a photoresponsivity of 14.3 mA/W, and a fast response speed
of 3.212/2.511 ms. It is worth noting that the fast varying optical
signal can be detected, even at a high frequency of 3500 Hz. More
importantly, the proposed CsPbCl<sub>3</sub> MWN photodetectors without
encapsulation demonstrate a remarkable operation stability over the
test in air ambient, can withstand a high working temperature of 373
K for 9 h continuous operation, and nearly 70% of the original photocurrent
of the photodetectors has been retained, further confirming the ultrastable
device operation. Note that this is the first report on high-temperature
operation behaviors of perovskite photodetectors. The results in this
study may promote the development of stable and high-efficiency perovskites
photodetectors compatibility for practical applications under harsh
conditions
Strategy of Solution-Processed All-Inorganic Heterostructure for Humidity/Temperature-Stable Perovskite Quantum Dot Light-Emitting Diodes
Recently, a pressing
requirement of solid-state lighting sources
with high performance and low cost has motivated increasing research
in metal halide perovskites. However, the relatively low emission
efficiency and poor operation stability of perovskite light-emitting
diodes (LEDs) are still critical drawbacks. In this study, a strategy
of solution-processed all-inorganic heterostructure was proposed to
overcome the emission efficiency and operation stability issues facing
the challenges of perovskite LEDs. Solution-processed n-ZnO nanoparticles
and p-NiO are used as the carrier injectors to fabricate all-inorganic
heterostructured CsPbBr<sub>3</sub> quantum dot LEDs, and a high-efficiency
green emission is achieved with maximum luminance of 6093.2 cd/m<sup>2</sup>, external quantum efficiency of 3.79%, and current efficiency
of 7.96 cd/A. More importantly, the studied perovskite LEDs possess
a good operation stability after a long test time in air ambient.
Typically, the devices can endure a high humidity (75%, 12 h) and
a high working temperature (393 K, three heating/cooling cycles) even
without encapsulation, and the operation stability is better than
any previous reports. It is anticipated that this work will provide
an effective strategy for the fabrication of high-performance perovskite
LEDs with good stability under ambient and harsh conditions, making
practical applications of such LEDs a real possibility
Photofacilitated Controllable Growth of ZnO Films Using Photoassisted Metal Organic Chemical Vapor Deposition
High-quality ZnO thin films were deposited on sapphire
substrates
using a photoassisted metal–organic chemical vapor deposition
(PA-MOCVD) system. A controllable morphology evolution with varying
degrees of crystallinity was observed. The microstructure of the film
changes from a three-dimensional nanorod form to two-dimensional continuous
dense form as the light irradiation intensity increases. A possible
photofacilitated nucleation mechanism with a higher nucleation rate
and density was proposed to explain the variation of the resulting
ZnO formation. In this case, the crystallinity and optical properties
of the epitaxial ZnO were also optimized, such that a low full width
at half-maximum (0.079°) of the rocking curve could be obtained,
similar to that of single-crystal ZnO. It was also found that the
tensile strain in the films could be availably relaxed by added thermal
energy and energetic photons provided by light irradiation. Additionally,
temperature-dependent photoluminescence results behaving as strong
exciton effects confirmed the relatively excellent quality of the
obtained ZnO films