4 research outputs found
Facile and Environmentally Friendly Solution-Processed Aluminum Oxide Dielectric for Low-Temperature, High-Performance Oxide Thin-Film Transistors
We
developed a facile and environmentally friendly solution-processed
method for aluminum oxide (AlO<sub><i>x</i></sub>) dielectrics.
The formation and properties of AlO<sub><i>x</i></sub> thin
films under various annealing temperatures were intensively investigated
by thermogravimetric analysis–differential scanning calorimetry
(TGA-DSC), X-ray diffraction (XRD), spectroscopic ellipsometry, atomic
force microscopy (AFM), attenuated total reflectance–Fourier
transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy
(XPS), impedance spectroscopy, and leakage current measurements. The
sol–gel-derived AlO<sub><i>x</i></sub> thin film
undergoes the decomposition of organic residuals and nitrate groups,
as well as conversion of aluminum hydroxides to form aluminum oxide,
as the annealing temperature increases. Finally, the AlO<sub><i>x</i></sub> film is used as gate dielectric for a variety of
low-temperature solution-processed oxide TFTs. Above all, the In<sub>2</sub>O<sub>3</sub> and InZnO TFTs exhibited high average mobilities
of 57.2 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> and 10.1 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, as well as an on/off current ratio of ∼10<sup>5</sup> and
low operating voltages of 4 V at a maximum processing temperature
of 300 °C. Therefore, the solution-processable AlO<sub><i>x</i></sub> could be a promising candidate dielectric for low-cost,
low-temperature, and high-performance oxide electronics
Degradation by Exposure of Coevaporated CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Thin Films
Degradation
of coevaporated CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> thin films
were investigated with X-ray photoelectron spectroscopy
and X-ray diffraction as the films were subjected to exposure of oxygen,
low pressure atmospheric air, atmospheric air, or H<sub>2</sub>O.
The coevaporated thin films have consistent stoichiometry and crystallinity
suitable for detailed surface analysis. The results indicate that
CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> is not sensitive to oxygen.
Even after 10<sup>13</sup> Langmuir (L, one L equals 10<sup>–6</sup> Torr s) oxygen exposure, no O atoms could be found on the surface.
The film is not sensitive to dry air as well. A reaction threshold
of about 2 × 10<sup>10</sup> L is found for H<sub>2</sub>O exposure,
below which no CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> degradation
takes place, and the H<sub>2</sub>O acts as an n-dopant. Above the
threshold, the film begins to decompose, and the amount of N and I
decrease quickly, leaving the surface with PbI<sub>2</sub>, hydrocarbon
complex, and O contamination
Characteristics of a Silicon Nanowires/PEDOT:PSS Heterojunction and Its Effect on the Solar Cell Performance
The interfacial energy-level alignment
of a silicon nanowires (SiNWs)/PEDOT:PSS heterojunction is investigated
using Kelvin probe force microscopy. The potential difference and
electrical distribution in the junction are systematically revealed.
When the PEDOT:PSS layer is covered at the bottom of the SiNW array,
an abrupt junction is formed at the interface whose characteristics
are mainly determined by the uniformly doped Si bulk. When the PEDOT:PSS
layer is covered on the top, a hyperabrupt junction localized at the
top of the SiNWs forms, and this characteristic depends on the surface
properties of the SiNWs. Because the calculation shows that the absorption
of light from the SiNWs and the Si bulk are equally important, the
bottom-coverage structure leads to better position matching between
the depletion and absorption area and therefore shows better photovoltaic
performance. The dependence of <i>J</i><sub>SC</sub> and <i>V</i><sub>OC</sub> on the junction characteristic is discussed
Nanoscale Insights into the Hydrogenation Process of Layered α‑MoO<sub>3</sub>
The hydrogenation process of the
layered α-MoO<sub>3</sub> crystal was investigated on a nanoscale.
At low hydrogen concentration,
the hydrogenation can lead to formation of H<sub><i>x</i></sub>MoO<sub>3</sub> without breaking the MoO<sub>3</sub> atomic
flat surface. For hydrogenation with high hydrogen concentration,
hydrogen atoms accumulated along the <101> direction on the
MoO<sub>3</sub>, which induced the formation of oxygen vacancy line
defects.
The injected hydrogen atoms acted as electron donors to increase electrical
conductivity of the MoO<sub>3</sub>. Near-field optical measurements
indicated that both of the H<sub><i>x</i></sub>MoO<sub>3</sub> and oxygen vacancies were responsible for the coloration of the
hydrogenated MoO<sub>3</sub>, with the latter contributing dominantly.
On the other hand, diffusion of hydrogen atoms from the surface into
the body of the MoO<sub>3</sub> will encounter a surface diffusion
energy barrier, which was for the first time measured to be around
80 meV. The energy barrier also sets an upper limit for the amount
of hydrogen atoms that can be bound locally inside the MoO<sub>3</sub> <i>via</i> hydrogenation. We believe that our findings
has provided a clear picture of the hydrogenation mechanisms in layered
transition-metal oxides, which will be helpful for control of their
optoelectronic properties <i>via</i> hydrogenation