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Material based on hydrogel from rice-straw with high absorption capacity and slow water release was prepared by cryogenic method, using citric acid as cross-linker and without creating waste stream to the environment. The structure and properties of the material were characterized by SEM, XRD, FTIR and TGA method. The results showed that the largest water absorbency of the material reached 30.67g/g, 4.48 times higher than the original rice-straw. The material was able to slowly release water in 6 days at room temperature and return water absorption of 3.97 g/g when reusing the material. In addition, the material is biodegradable and biocompatible. With the obtained results and simple, inexpensive, environmentally friendly method, this is a material that can be industrially produced and widely used in green agriculture.

In this study, ZnO nanorods decorated with gold (Au) nanoparticles with the desired size parameters were fabricated using a simple, low-cost, and highly efficient method. The ZnO nanorod structure was fabricated using a hydrothermal method on a ZnO seed layer with hydrothermal solution concentrations varying from 20 mM to 90 mM. Au nanoparticles were coated on the ZnO nanorod structure by magnetron sputtering with a sputtering time from the 40s to 70 s. The characteristics of the fabricated samples were investigated through SEM images and optical absorption spectroscopy. The results show that the fabricated ZnO nanorods are relatively uniform, with a cylindrical shape and hexagonal cross-section when the solution concentration is less than 70 mM. Au nanoparticles were attached to the surface of the ZnO nanorods with average sizes of 30-50 nm. The optical absorption spectroscopy results showed that the ZnO nanorods’ absorption edge appeared at a wavelength of approximately 395 nm. In addition, the exciton absorption peak of Au nanoparticles was between 550 nm and 600 nm and there was a shift towards shorter wavelengths as the size of the Au nanoparticle decreased. This result opens up potential applications of this material such as increasing photocatalytic efficiency and its, use in photonic devices, etc.

High-performance low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) have been developed for larger applications than flat panel displays (FPDs) such as three-dimensional integrated circuits (3D-ICs) and glass sheet computers. The crystallinity of poly-Si thin films has been the key factor determining TFTs’ performance. In this work, a void-defect location has been controlled by patterning amorphous silicon (a-Si) thin films with rectangular and square holes before crystallized by multiline continuous-wave laser beam to avoid the effect of void-defects on the TFTs’ performance. Instead of randomly appearing in the poly-Si thin films, void-defects were only observed at the backsides of the patterned holes. Interestingly, large crystal grains without void-defects were laterally crystallized at Si strips between holes. By observing the crystallinities of poly-Si thin film around the patterned holes, both the mechanism of the void formation and crystal growth based on temperature gradient was clarified.

Few layer graphene (FLG) was synthesized by $\mu$-wave assisted exfoliation of expanded graphite in toluene with an overall yield from c.a. 7% to 20%. A significant difference in the absorption of $\mu$-waves by the expanded graphite and toluene allowed a rapid heating of the medium. The number of FLG sheets varies from 3 to 12, while the lateral size of the sheets exceeds few $\mu$ms. The obtained FLG exhibits very low resistance with average value of 1.6 k$\Omega$ (500 $\Omega$ minimum) which is comparable to that of high quality graphenes synthesized by CVD methods, and lower than numbers of exfoliated graphenes.

Background: The active layer not only must have a strong light absorption in the visible spectrum but must also be sufficient for charge carrier transport to the electrodes. Electrons in conducting polymer transport by hopping between different energy levels resulted in much lower charge mobility. Therefore, the thickness of the active layer must be limited, so the separated charge can reach the corresponding electrodes without recombination. However, a thin active layer has weaker light absorption, resulting in the low photogenerated current in organic solar cell devices. Furthermore, buffer layers usually have high charge mobility, which in turn would enhance the transportation of charge from the active layer to electrodes. Metal oxides have been studied to be used as a cathode buffer layer, such as titanium dioxide (TiO2), zinc oxide (ZnO), etc. Objective: In this work, behaviors of the photon-electrical characteristics with variation in thickness of the active (poly(3-hexylthiophene-2,5-diyl) and phenyl-C61 butyric acid methyl ester blend) and buffer (zinc oxide) layers were investigated. Methods: The influences of the thickness of the active and buffer layers on characteristic parameters of organic solar cells were investigated by solving the drift and diffusion equation with the photogenerated current given by the Hetch equation. Results: The optimum thickness was obtained around 100 nm and below 10 nm for the active and the ZnO buffer layers, respectively. Conclusion: Thinner active layer resulted in lower photocurrent due to poor light absorption while at 150 nm thick and above, PCE of the device reduced rapidly because of the high recombination rate of photogenerated electron-hole pairs. ZnO buffer layer was used as an electron transport layer and a hole blocking layer in order to improve the cell’s performance. The addition of ZnO enhanced the PCE up to 2.48 times higher than the conventional device.

Zinc oxide is known as an excellent material for biosensors, solar cells, semiconductors and photocatalysts. In this work, n-ZnO nanorods/p-Si heterostructures were successfully fabricated by a hydrothermal method at different baking temperatures. The n-ZnO nanorods/p-Si heterostructures show good photocatalytic ability at high baking temperature. The concentration of Rhodamine B can be decreased up to 97% after 150 min treated by the n-ZnO nanorods/p-Si heterostructures grown at 80 oC. This result indicates that the n-ZnO nanorods/p-Si heterostructures are capable of being used in the decomposition of organic compounds.

Background:: Optical reflection loss can be reduced more than 30% when multilayers ARC are deposited on the optoelectronic devices surface. Besides that, sub-wavelength structures, which have a period sufficiently smaller than the wavelength of light, have been introduced as an antireflection layer to offer a new possibility to suppress the Fresnel reflection. Normally, e-bean and nano-imprint lithography techniques are used to create nano-scale etch mask patterns. Metallic nanoparticles, which can be formed by a thermal dewetting process of metal thin film without any nanolithography techniques, can be utilized as an etch mask for the nano structure fabrications. The nano-patterned structures were fabricated on a silicon nitride passivation layer of a GaInP/GaAs/Ge triple-junction solar cell and showed an enhancement of its performance due to improved optical transmission and current matching. Objective:: Investigate the influences of InGaP nano-pattern structures on the optical characteristics and applied for compound solar cells. Method:: In this report, disordered InGaP nano-pattern structures were formed by thermally dewetted Au nanoparticles and anisotropic dry etching processes. The effects of the InGaP nano-patterned structure on the optical reflection characteristics were investigated. Results:: The result indicated that the InGaP nano-patterned structure can reduce the optical reflection in a wide range of wavelengths and, thus, can work as an antireflection layer. The InGaP nanostructure can improve up to 14.8% in the short circuit current density compared to that of the planar cell. Conclusion:: The InGaP nano structures have been successfully fabricated by thermal dewetted Au nanoparticles and anisotropic dry etching methods. The fabricated Au nanoparticles pattern was found to be the best when annealing temperature is 400°C for 30 minutes with the 5nm thick of Au film. By controlling dry etching time, the height of InGaP nanostructures can be varied from 95 nm to 150 nm. With the increasing of the height, the optical reflectance can be down to 22%. The InGaP nanostructure with the height of 150 nm was also introduced to the window layer of a single junction GaAs soar cell. The result indicated that the InGaP nanostructure only affects on the short circuit current density.