Lead-based halide perovskites (APbX3, where A = organic
or inorganic cation, X = Cl, Br, I) are suitable materials for many
optoelectronic devices due to their many attractive properties. However,
the concern of lead toxicity and the poor ambient and operational
stability of the organic cation group greatly limit their practical
utilization. Therefore, there has recently been great interest in
lead-free, environment-friendly all-inorganic halide perovskites (IHPs).
Sb and Sn are common species suggested to replace Pb for Pb-free IHPs.
However, the large difference in the melting points of the precursor
materials (e.g., CsBr and SbBr3 precursors for Cs3Sb2Br9) makes the chemical vapor deposition
(CVD) growth of high-quality Pb-free IHPs a very challenging task.
In this work, we developed a two-step CVD method to overcome this
challenge and successfully synthesized Pb-free Cs3Sb2Br9 perovskite microplates. Cs3Sb2Br9 microplates ∼25 μm in size with
the exciton absorption peak at ∼2.8 eV and a band gap of ∼2.85
eV were obtained. The microplates have a smooth hexagonal morphology
and show a large Stokes shift of ∼450 meV and exciton binding
energy of ∼200 meV. To demonstrate the applications of these
microplates in optoelectronics, simple photoconductive devices were
fabricated. These photodetectors exhibit a current on/off ratio of
2.36 × 102, a responsivity of 36.9 mA/W, and a detectivity
of 1.0 × 1010 Jones with a fast response of rise and
decay time of 61.5 and 24 ms, respectively, upon 450 nm photon irradiation.
Finally, the Cs3Sb2Br9 microplates
also show good stability in ambient air without encapsulation. These
results demonstrate that the 2-step CVD process is an effective approach
to synthesize high-quality all-inorganic lead-free Cs3Sb2Br9 perovskite microplates that have the potential
for future high-performance optoelectronic device applications.
Oxide-based transparent p−n homojunctions are desirable for the development of transparent electronics. However, most oxide semiconductors are intrinsically n-type and to achieve p-type wide-gap oxide is still challenging. Previously, we have demonstrated that alloying a high-mobility n-type material such as CdO with p-type NiO can provide an avenue for electronic band engineering and consequently achieve bipolar conductivity in the midalloy composition. In this study, we synthesized O-rich Ni x Cd 1−x O alloys (Ni x Cd 1−x O 1+δ ) over the entire composition with Li and Cu doping using radio frequency (RF) magnetron sputtering at room temperature. We show that by Li and Cu doping the conductivity in the p-type regime of these alloys is improved, which also leads to a wider composition window for bipolar doping in Ni x Cd 1−x O. Specifically, by Li doping, the p-type alloy composition can be extended to x ≥ 0.3 so that the bipolar doping window is expanded to 0.30 ≤ x ≤ 0.52. Detailed measurements on electrical, structural, optical, and electronic properties suggest that Li is an effective acceptor, offering a promising way to improve the p-type conduction in Ni-rich Ni x Cd 1−x O alloys as well as to regulate the bipolar conductivity in this alloy system. A p-Ni 0.7 Cd 0.3 O:Li/n-Ni 0.45 Cd 0.55 O quasi-homojunction was fabricated and a rectification ratio ∼10 2 with an ideality factor of ∼2.9 was obtained. The demonstrated quasi-homojunction structure also showed >60% transmittance in the visible spectrum.
Lead-based organic or inorganic halide perovskites (ABX3, A= organic or inorganic cation, B= lead cation, and X= Cl, Br, I) are well-known for their excellent properties and technologically suitable for...
Due
to their low-temperature deposition, high mobility (>10 cm2/V·s), and electrical conductivity, amorphous ionic oxide
semiconductors (AIOSs) have received much attention for their applications
in flexible and/or organic electro-optical devices. Here, we report
on a study of the flexibility of CdO-In2O3 alloy
thin films, deposited on a polyethylene terephthalate (PET) substrate
by radio frequency magnetron sputtering at room temperature. Cd1–x
In
x
O1+δ alloys with the composition of x > 0.6 are amorphous, exhibiting a high electron mobility of 40–50
cm2/V·s, a low resistivity of ∼3 × 10–4 Ω·cm, and high transmittance over a wide
spectral window of 350 to >1600 nm. The flexibility of both crystalline
and amorphous Cd1–x
In
x
O1+δ films on the PET substrate
was investigated by measuring their electrical resistivity after both
compressive and tensile bending with a range of bending radii and
repeated bending cycles. Under both compressive and tensile bending
with R
b = 16.5 mm, no significant degradation
was observed for both the crystalline and amorphous films up to 300
bending cycles. For a smaller bending radius, the amorphous film shows
much less electrical degradation than the crystalline films under
compressive bending due to less film delamination at the bending sites.
On the other hand, for a small bending radius (<16 mm), both crystalline
and amorphous films degrade after repeated tensile bending, most likely
due to the development of microcracks in the films. To demonstrate
the application of amorphous Cd1–x
In
x
O1+δ alloy in photovoltaics,
we fabricated perovskite and bulk-heterojunction organic solar cells
(OSCs) on glass and flexible PET utilizing amorphous Cd1–x
In
x
O1+δ layers as transparent electrodes. The organic–inorganic hybrid
perovskite solar cells (PSCs) exhibit a power conversion efficiency
(PCE) of ∼11 to 12% under both front and back illumination,
demonstrating good bifacial performance with bifaciality factor >90%.
The OSCs fabricated on an amorphous Cd1–x
In
x
O1+δ-coated
flexible PET substrate achieve a promising PCE of 12.06%. Our results
strongly suggest the technological potentials of amorphous Cd1–x
In
x
O1+δ as a reliable and effective transparent conducting
material for flexible and organic optoelectronic devices.
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