Liang-Yih Chen

Organometal halide perovskite solar cells: degradation and stability

Organometal halide perovskite solar cells have evolved in an exponential manner in the two key areas of efficiency and stability. The power conversion efficiency (PCE) reached 20.1% late last year. The key disquiet was stability, which has been limiting practical application, but now the state of the art is promising, being measured in thousands of hours. These improvements have been achieved through the application of different materials, interfaces and device architecture optimizations, especially after the investigation of hole conductor free mesoporous devices incorporating carbon electrodes, which promise stable, low cost and easy device fabrication methods. However, this work is still far from complete. There are various issues associated with the degradation of Omh-perovskite, and the interface and device instability which must be addressed to achieve good reproducibility and long lifetimes for Omh-PSCs with high conversion efficiencies. A comprehensive understanding of these issues is required to achieve breakthroughs in stability and practical outdoor applications of Omh-PSCs. For successful small and large scale applications, besides the improvement of the PCE, the stability of Omh-PSCs has to be improved. The causes of failure and associated mechanisms of device degradation, followed by the origins of degradation, approaches to improve stability, and methods and protocols are discussed in detail and form the main focus of this review article.

Controlled Synthesis of CdSe Quantum Dots by a Microwave-Enhanced Process: A Green Approach for Mass Production

A method that does not employ hot-injection techniques has been developed for the size-tunable synthesis of high-quality CdSe quantum dots (QDs) with zinc blende structure. In this environmentally benign synthetic route, which uses less toxic precursors, solvents, and capping ligands, CdSe QDs that absorb visible light are obtained. The size of the as-prepared CdSe QDs and thus their optical properties can be manipulated by changing the microwave reaction conditions. The QDs were characterized by XRD, TEM, UV/Vis, FTIR, time-resolved fluorescence spectroscopy, and fluorescence spectrophotometry. In this approach, the reaction is conducted in open air and at a much lower temperature than in hot-injection techniques. The use of microwaves in this process allows for a highly reproducible and effective synthesis protocol that is fully adaptable for mass production and can be easily employed to synthesize a variety of semiconductor QDs with the desired properties. Possible applications of the CdSe QDs were assessed by deposition on TiO(2) films.

Innovative fabrication of a Au nanoparticle-decorated SiO2 mask and its activity on surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) utilizing the well-defined localized surface plasmon resonance (LSPR) of Ag and Au nanoparticles (NPs) under resonant irradiation has emerged as a promising spectroscopy technique for providing vibrational information on trace molecules. The Raman scattering intensity from molecules close to the surface of these finely divided metals can be significantly enhanced by a factor of more than 10(6). In addition to the high sensitivity, the reproducibility of the SERS signal is also an important parameter for its reliable application. In this work, we report on the innovative and facile fabrication of a Au NP-decorated SiO2 mask coated on indium tin oxide (ITO) glass as a SERS array substrate. First, a highly ordered porous SiO2 mask with pore sizes of 350 nm in diameter and wall thickness of 60 nm was deposited on ITO glass by using spin coating. Then, Au NPs were controllably decorated into the pores of the conductive ITO glass-bottomed SiO2 mask by using sonoelectrochemical deposition-dissolution cycling (SEDDC). Experimental results indicate that the SERS effect of Rhodamine 6G (R6G) observed on this developed substrate increases with an increase in the deposition time of Au NPs in SEDDC. The corresponding optimal enhancement factor (EF) that is obtained is ca. 6.5 × 10(7). Significantly, this system achieves an optimal reproducibility under a medium-length deposition time of Au NPs in SEDDC with a relative standard deviation (RSD) of 12% for measurements of five spots on different areas. The low RSD of the SERS signal and the large EF suggest that the developed array system can serve as an excellent spectroscopy platform for practical applications in analytical chemistry.

Quantitative evaluation on activated property-tunable bulk liquid water with reduced hydrogen bonds using deconvoluted raman spectroscopy

Interesting properties of water with distinguishable hydrogen-bonding structure on interfacial phase or in confined environment have drawn wide attentions. However, these unique properties of water are only found within the interfacial phase and confined environment, thus, their applications are limited. In addition, quantitative evaluation on these unique properties associating with the enhancement of waters physical and chemical activities represents a notable challenge. Here we report a practicable production of free-standing liquid water at room temperature with weak hydrogen-bonded structure naming Au nanoparticles (NPs)-treated (AuNT) water via treating by plasmon-induced hot electron transfer occurred on resonantly illuminated gold NPs (AuNPs). Compared to well-known untreated bulk water (deionized water), the prepared AuNT water exhibits many distinct activities in generally physical and chemical reactions, such as high solubilities to NaCl and O2. Also, reducing interaction energy within water molecules provides lower overpotential and higher efficiency in electrolytic hydrogen production. In addition, these enhanced catalytic activities of AuNT water are tunable by mixing with deionized water. Also, most of these tunable activities are linearly proportional to its degree of nonhydrogen-bonded structure (DNHBS), which is derived from the O-H stretching in deconvoluted Raman spectrum.

Uniform GaN thin films grown on (100) silicon by remote plasma atomic layer deposition

The growth of uniform gallium nitride (GaN) thin films was reported on (100) Si substrate by remote plasma atomic layer deposition (RP-ALD) using triethylgallium (TEG) and NH3 as the precursors. The self-limiting growth of GaN was manifested by the saturation of the deposition rate with the doses of TEG and NH3. The increase in the growth temperature leads to the rise of nitrogen content and improved crystallinity of GaN thin films, from amorphous at a low deposition temperature of 200 °C to polycrystalline hexagonal structures at a high growth temperature of 500 °C. No melting-back etching was observed at the GaN/Si interface. The excellent uniformity and almost atomic flat surface of the GaN thin films also infer the surface control mode of the GaN thin films grown by the RP-ALD technique. The GaN thin films grown by RP-ALD will be further applied in the light-emitting diodes and high electron mobility transistors on (100) Si substrate.

Triggering comprehensive enhancement in oxygen evolution reaction by using newly created solvent

Theoretical calculations indicate that the properties of confined liquid water, or liquid water at surfaces, are dramatically different from those of liquid bulk water. Here we present an experimentally innovative strategy on comprehensively efficient oxygen evolution reaction (OER) utilizing plasmon-induced activated water, creating from hot electron decay at resonantly illuminated Au nanoparticles (NPs). Compared to conventional deionized (DI) water, the created water owns intrinsically reduced hydrogen-bonded structure and a higher chemical potential. The created water takes an advantage in OER because the corresponding activation energy can be effectively reduced by itself. Compared to DI water-based solutions, the OER efficiencies at Pt electrodes increased by 69.3%, 21.1% and 14.5% in created water-based acidic, neutral and alkaline electrolyte solutions, respectively. The created water was also effective for OERs in photoelectrochemically catalytic and in inert systems. In addition, the efficiency of OER increased by 47.5% in created water-based alkaline electrolyte solution prepared in situ on a roughened Au electrode. These results suggest that the created water has emerged as an innovative activator in comprehensively effective OERs.

Enhancing the insulation of wide-range spectrum in the PVA/N thin film by doping ZnO nanowires

In this study, polyvinyl alcohol/nitrogen (PVA/N) hybrid thin films doped with sharp-sword ZnO nanowires with insulating effect and wide-range spectrum are demonstrated for the first time. PVA/N doped ZnO nanocomposites were developed by blending PVA and N-doped ZnO nanowires in water at room temperature. Measurements from the field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Raman, and photoluminescence emission (PL) spectra of the products show that nitrogen is successfully doped into the ZnO wurtzite crystal lattice. In addition, the refractive index of PVA/N doped ZnO hybrid thin films can be controlled by varying the doped ZnO nanowires under different NH3 concentrations. It is believed that PVA/N doped ZnO hybrid thin films are a suitable candidate for emerging applications like heat-shielding coatings on smart windows.

Synthesis CdSe(x)S(1-x) core/shell type quantum dots via one injection method.

The photoluminescence quantum yield (PL-QY) of ternary colloidal CdSe(x)S(1-x) quantum dots (QDs), which were prepared by a one-injection method, enhances with increasing S content. The possible enhancement mechanism was explored by structural analysis via X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Both found that the enhancement of PL-QY of ternary CdSe(x)S(1-x) QDs strongly correlated with self-formed core/shell conformation in the non-coordination solution.

Identification of the physical origin behind disorder, heterogeneity, and reconstruction and their correlation with the photoluminescence lifetime in hybrid perovskite thin films

Organolead halide perovskites are an impressive and relatively recent class of light-absorbing materials for solar cells and light-emitting devices. It has been reported that exposure of perovskite materials to light has negative impacts on device performance. Also, surface recombination has been reported as a major obstacle to the total carrier lifetime in perovskite polycrystalline thin films. Herein, we explored the role played by nanosecond pulsed UV laser-irradiation in carrier dynamics in perovskite thin films. Steady-state and time-resolved photoluminescence measurements revealed the interplay of disorder and heterogeneity on photoexcited carrier dynamics, while in situ micro Raman spectroscopy and angle dispersive X-ray diffraction showed the mechanisms of crystal phase reconstruction. Exposure to laser light leads to rapid crystal phase reconstruction and hence, unexpectedly, extends the PL lifetime by fourfold instead of promoting degradation. This verifies that nanosecond pulsed laser irradiation plays a beneficial role in improving optoelectronic material parameters. Our findings reveal that pulsed laser irradiation is a new approach to the reconstruction of the microstructure and offers beneficial effects in the manufacture of perovskite solar cells. Moreover, this work provides a clear insight towards identifying the physical origin behind the disorder, heterogeneity, film reconstruction and nano-structuring as well as their correlation with improved PL lifetimes.

CHAPTER 9:Methods for the X-Ray Diffraction Patterns of Nanocalcium in Milk

In the first section of this chapter, the function of calcium in the human body, food nanotechnology, and several traditional analyzed methods for nanocalcium were described. The normal methods could determine the concentrations of nanocalcium additives in food and the analytic species is in ionic or ionized state. However, it is not easy to evaluate the sources of the calcium salt. To find the correct structures of added calcium salts, it would be one of the important issues to identify the phase transformation of the calcium during any treatments. X-ray diffraction technology can provide useful structural information of any crystals to detect the quantities of additives in the nanofood or identify the phase variation of food treated by different procedures. Therefore, the basic fundamental principles of the X-ray diffraction technology are shown in the second section. The content of the third section further probes into the crystal structures of nanocalcium additives in milk powders in the recent market. The X-ray diffraction patterns of the milk samples with the addition of nanocalcium have been obtained to evaluate the crystal phase and its structure transformation. In addition, the results also inferred that the milk powders containing nanocalcium after processing would prompt the transformation of crystal structure to partially generate oxide structures or even hydroxide structures. These trends make the mean of structure information of the nanocalcium additives more complicated. Herein, this chapter provides a simple methodology by using the X-ray diffraction technology to carry out the structural identification of the nanocalcium additives in milk powders. It can effectively characterize the phases of components and also reveal the structural stability of the nanoscale additives in food nanotechnology.