The direct emission of circularly polarized (CP) light improves the efficiency of an organic light-emitting diode and characterizes the secondary structure of proteins. In most cases, CP light is generated from a luminescent layer containing chiral characteristics, thereby generating only one kind of CP light in an entire device. Here, we propose direct CP light emissions using a twisted achiral conjugate polymer without any chiral dopant as an emitting layer (EML). The twisted structure is induced in the mesogenic conjugate polymer due to its elasticity by applying different alignment directions to its upper and lower interfaces. Furthermore, we demonstrate the simultaneous emission of orthogonal CP light in a single luminescent device by patterning different alignment directions on the surfaces of the EML. The light source with multipolarization including the orthogonal CP states is applicable to many applications in biosensors and optical devices.

Micro-cavity top-emitting organic light emitting diodes (TEOLEDs) are now receiving prominence as a technology for the active matrix display applications. The semi-transparent metal cathode plays the crucial role in realizing TEOLEDs structure. Here, we report the optimization results on Mg:Ag ratio as the semitransparent cathode deposited by vacuum thermal evaporation. The optimized Mg:Ag cathode with 1:10 ratio (wt %) shows a sheet resistance value as low as 5.2 Ω/□, an average transmittance of 49.7%, reflectance of 41.4%, and absorbance of 8.9% over the visible spectral region (400~700 nm). The fabricated red TEOLEDs device implemented using LiF (1nm)/Mg:Ag (1:10) cathode shows the voltage value of 4.17 V at a current density of 10.00 mA/cm, and current efficiencies variation from 55.3 to 50.1 cd/A over the brightness range 2,000 - 12,000 cd/m. The electroluminescence (EL) spectrum displays the light emission at 608 nm wavelength with a half width of 29.5 nm. The narrow half-width of red light emission is attributed to the micro-cavity effects due to the semitransparent cathode.

Flat and homogeneous films by ink jet printing of organic materials are proven to be essential for OLED application. The impact of ink formulation, film thickness, pixel size, bank layout and process conditions (i.e. drying parameters) have been investigated. Their severe impact on device performance is illustrated.

We report an improved 3-stacked white organic light emitting diode (WOLED) structure comprised of layers emitting red and yellow-green phosphorescence in the 2nd stacked device. We focused on developing the WOLED devices to realize 4K premium OLED TV displaying very high brightness and excellent color characteristics, with the optimized color layer. The WOLED has a high current efficiency of 83 cd/A, and cool white color whose color coordinate is (0.297, 0.317). 65-inch 4K premium OLED TV employing the new WOLED shows 800 nit of peak brightness, and 99 percent color gamut in DCI color space.

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