Effects of MEH-PPV Molecular Ordering in the Emitting Layer on the Luminescence Efficiency of Organic Light-Emitting Diodes.

We investigated the effects of molecular ordering on the electro-optical characteristics of organic light-emitting diodes (OLEDs) with an emission layer (EML) of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). The EML was fabricated by a solution process which can make molecules ordered. The performance of the OLED devices with the molecular ordering method was compared to that obtained through fabrication by a conventional spin coating method. The turn-on voltage and the luminance of the conventional OLEDs were 5 V and 34.75 cd/m2, whereas those of the proposed OLEDs were 4.5 V and 120.3 cd/m2, respectively. The underlying mechanism of the higher efficiency with ordered molecules was observed by analyzing the properties of the EML layer using AFM, SE, XRD, and an LCR meter. We confirmed that the electrical properties of the organic thin film can be improved by controlling the molecular ordering of the EML, which plays an important role in the electrical characteristics of the OLED.

Reflective Bistable Chiral Splay Nematic Liquid Crystal for Low-Power Heat Sensor.

The memory effect of the bistable liquid crystal mode is able to maintain the display information for a long time. The splay state and π twist states are used as the memory states of the bistable chiral splay nematic (BCSN) mode. The transition time from the π twist state to the splay state is sensitive to the temperature. In this paper, for the heat sensor application, the reflective structure of the BCSN mode has been studied by the Jones matrix method. In experiments, the measured contrast ratio can be over 200 with a minimal reflective structure including a single polarizer and a reflector.

Crosstalk-free dual-view liquid crystal display using patterned E-type polarizer.

We present a dual-view liquid crystal display that allows two faces of the display to be viewed in opposite directions to show different image/video content simultaneously. This device is characterized by a two-domain twisted nematic liquid crystal and a patterned E-type polarizer. Its key optical performance, including the voltage-luminance curve, crosstalk, and viewing angle, has been investigated. When observed at the best viewing angle, the crosstalk between the right and left views is less than 0.07% for all grayscales. In addition, this type of crosstalk can be immune to the misalignment between the polarizers and the liquid crystal layer. For each right/left view, the range of the viewing angle spans roughly 50°.

Visual evaluation of surface anchoring strength by electrohydrodynamic convection of a nematic liquid crystal.

Visual evaluation of the surface anchoring energies in a nematic liquid crystal (LC) cell is characterized by the direction of the convection roll pattern that appears in the low-frequency conduction regime. The convection roll pattern in a twisted nematic LC (TNLC) cell is oriented perpendicular to the midplane LC director dominating the direction of convection flow, and its direction is determined by the relative surface anchoring energy between two surface boundaries. Thus the direction of the roll pattern generated at the TNLC cell with asymmetric LC alignment layers can provide information on the surface anchoring energies at the two boundaries. We demonstrate a method for determining the two anchoring energies through a measured midplane LC director applied to the Ericksen-Leslie equation.

Effects of electron transport material on blue organ light-emitting diode with fluorescent dopant of BCzVBi.

High efficiency blue organic light emitting diodes (OLEDs), based on 2-me-thyl-9,10-di(2-naphthyl) anthracene (MADN) doped with 4,4'-bis(9-ethyl-3-carbazovinylene)-1,1'-biphenyl (BCzVBi), were fabricated using two different electron transport layers (ETLs) of tris(8-hydroxyquinolino)-aluminum (Alq3) and 4,7-di-phenyl-1,10-phenanthroline (Bphen). Bphen ETL layers favored the efficient hole-electron recombination in the emissive layer of the BCzVBi-doped blue OLEDs, leading to high luminous efficiency and quantum efficiency of 8.34 cd/A at 100 mA/cm2 and 5.73% at 100 cd/m2, respectively. Maximum luminance of blue OLED with Bphen ETL and Alq3 ETL were 10670 cd/m2, and CIExy coordinates of blue OLEDs were (0.180, 0279) and (0.155, 0.212) at 100 cd/m2.

Optimal design of omni-directional viewing angle switching panel.

A viewing angle switching (VAS) panel used for the conversion of wide and narrow viewing angle has been demonstrated. Unlike the previous VAS panels, this one features a pair of same-handed circular polarizers and it is capable of switching the viewing angle omni-directionally from wide to narrow or vice versa by electrically controlling the birefringence effect of the LC layer which is sandwiched in between. To explain how it works, the design principle as well as the optimization of both wide and narrow viewing modes will be elaborated hereinafter.