4 research outputs found

    Facile and Environmentally Friendly Solution-Processed Aluminum Oxide Dielectric for Low-Temperature, High-Performance Oxide Thin-Film Transistors

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    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

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    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

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    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>

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    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
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