Square Column Structure of High Efficiency, Reliable, Uniformly Flexible LED Devices

This study demonstrates that flexible white LEDs, doped with diffusion particles and with a square column structure, have excellent luminosity, uniformity, and bending reliability. This large area (5 cm × 5 cm) square column flexible device had a smaller thickness (2 mm), and enhancements in both luminous efficiency (29.5%) and uniformity (44.6%) compared to the characteristics of the 6 mm reference sample. Optimization of the reflective layer coating for the square column, flexible white LED was achieved with a higher luminous efficiency (171 lm/w) and uniformity (92%). We designed a novel lightning bolt electrode to improve reliability and bendability. After the bending test, the blue flexible LED had a lower bending diameter (10 mm) but more bending circles (increased to 2000 times.

OPTICAL FIBER LOSS ANALYSIS FOR AN APPLICATION OF SPECTROPHOTOMETER SYSTEM

Loss analysis due to the insertion of optical fiber in short wavelength spectrophotometer system is experimentally conducted to improve resolution and flexibility of the system design. In this paper, type, length and bending diameter of the optical fiber are analyzed as a preliminary work towards the development of a low-loss spectrophotometer system. In order to analyze a suitable type of fiber to be adopted in this system, a 20 mm length and 0 mm bending diameter of a single-mode fiber (SMF), multi-mode fiber (MMF) and Polymethyl methacrylate (PMMA) fiber are tested. The length and bending diameter of the suitable fiber is then varied from 20 mm to 60 mm and 6 mm to 22 mm respectively. In this paper, light emitting diode (LED) centered at 525 nm wavelength with 35 nm full width half maximum (FWHM) is used as the spectrophotometer light source while silicon photodiode is used as the detector. In this work, photodetector output voltage is recorded to analyze the loss contributed by these three parameters. At this particular wavelength, PMMA is found to be a suitable fiber to be adopted due to its minimal loss performance. Besides the fiber type, having a minimal fiber length with maximal fiber bending diameter can reduce loss due to the insertion of optical fiber in spectrophotometer system, hence improving the spectrophotometer resolution performance.

Influence of Mechanical Alloying on the Behavior of Fe-Mn-Si-Cr-Ni Shape Memory Alloys Made by Powder Metallurgy

Fe-14 Mn-6 Si-9 Cr-5 Ni (mass. %) shape memory alloys (SMAs) were produced from raw powders employed both in initial commercial state and in a mixture state of equal fractions of commercial and mechanically alloyed (MA’d) particles. After blending, pressing and sintering, powder compacts were hot rolled (HR’d) and solution treated (ST’d) before being machined into plane-parallel lamellas. Specimens with special geometry were pre-strained on a tensile testing machine. By means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) the presence of ε hexagonal close packed and α’ body center cubic stress induced martensites was revealed and their thermally induced reversion to γ face center cubic austenite was evaluated by modulated differential scanning calorimetry (MDSC). The results enabled the study of the influence of MA, HR, ST and pre-straining on phase structure and associated on shape memory effect (SME). The lamellas were hot formed into rings, which were trained in bending. Diameter reduction of trained enlarged rings, on heating, was monitored by cinematographic analysis.

Comparisons of the Mechanical Behaviors of Poly (3, 4-ethylenedioxythiophene) (PEDOT) and ITO on Flexible Substrates

ABSTRACTIndium Tin Oxide (ITO) has been widely used as a Transparent Conductive Oxide (TCO) layer in the photovoltaic solar technology because of its excellent electrical and optical properties. However, ITO is brittle, and its conductivity decreases significantly as the ITO films are exposed to stretching or bending strains especially in flexible/foldable solar cell applications. The cracks in ITO appear at very low strains which might cause failure in the conductive layer because of the combination of a very thin film of brittle ceramic material applied to a polymer substrate. Poly (3, 4-ethylenedioxythiophene), abbreviated PEDOT, is of increasing interest as a competitive candidate to ITO. PEDOT has found its way in many applications such as transparent electrode materials and transparent conductive layers in photovoltaic solar cells. In this work, the mechanical behavior of PEDOT was studied under high cycle bending fatigue in which the effects of bending diameter and bending frequency were considered and compared to ITO. High magnification optical images were used to study cracking in the PEDOT as well as the ITO layers. In flexible solar cells, the web will be exposed to folding/bending many times during manufacturing and installation. Therefore, the thin film substrate structure will be exposed to cyclic loading cyclic tensile and compressive strains. Therefore, this work was designed to mechanically fatigue the structure and study its behavior. It was found that bending diameters as well as material (PEDOT or ITO) have a great influence on the electrical conductivity of the thin films.