We demonstrate selectively enhanced emission by controlling the intrachain and interchain excitons of a conjugated polymer through adjusting surface plasmons. Enhanced light emission from the intrachain excitons was observed by coupling the localized surface plasmon resonance with the intrachain band of the conjugated polymer using Ag nanoparticles. Light emission from the interchain excitons was enhanced by exploiting both the increased strength of the interchain dipole due to the image dipole and the coupling between excitons and surface plasmon polaritons (SPPs). As the Ag nanostructures become complete films, light emission from the interchain excitons increased.

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We synthesized cesium lead-halide perovskite colloidal nanocrystals using the hot injection method for wide-color-gamut low-cost displays. An efficient surface defect passivation technique was applied to further improve the optical performance of the green and red perovskite nanocrystals. The prepared perovskite nanocrystal solutions were formulated into inkjet printable homogeneous inks and uniformly printed on the substrate with appropriate surface control. They formed the wide-color-gamut color conversion layers of quantum dot organic light-emitting diode displays. We confirmed the excellent photophysical properties of the synthesized green/red perovskite nanocrystals and the inkjet printed color conversion layers with a photoluminescence quantum yield of 99.7%/96.2% and a wide color reproduction range of 117%.

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Optimization of ink-jet printing conditions of quantum-dot (QD) ink by cosolvent process and improvement of quantum-dot light-emitting diodes (QLEDs) characteristics assisted by vacuum annealing were analyzed in this research. A cosolvent process of hexane and ortho-dichlorobenzene (oDCB) was optimized at the ratio of 1:2, and ink-jetting properties were analyzed using the Ohnesorge number based on the parameters of viscosity and surface tension. However, we found that these cosolvents systems cause an increase in the boiling point and a decrease in the vapor pressure, which influence the annealing characteristics of the QD emission layer (EML). Therefore, we investigated QLEDs’ performance depending on the annealing condition for ink-jet printed QD EML prepared using cosolvents systems of hexane and oDCB. We enhanced the quality of QD EML and device performance of QLEDs by a vacuum annealing process, which was used to prevent exposure to moisture and oxygen and to promote effective evaporation of solvent in QD EML. As a result, the characteristics of QLEDs formed using ink-jet printed QD EML annealed under vacuum environment increased luminescence (L), current efficiency (CE), external quantum efficiency (EQE), and lifetime (LT50) by 30.51%, 33.7%, 21.70%, and 181.97%, respectively, compared to QLEDs annealed under air environment.

In this study, we introduce optimization of the annealing conditions for improvement of hardness and hole transporting properties of high-molecular weight poly [9, 9-dioctylfluorene-co-N-(4-(3-methylpropyl)) diphenylamine] (TFB) film used as a Hole Transport Layer (HTL) of Quantum-dot Light-emitting Diodes (QLEDs). As annealing temperatures were increased from 120 °C to 150 °C or more, no dissolving or intermixing phenomena at the interface between HTL and Quantum-Dot Emission Layer (QDs EML) was observed. However, when the annealing temperatures was increased from 150 °C to 210 °C, the intensity of the absorbance peaks as determined by Fourier Transform Infrared (FT-IR) measurement was found to relatively decrease, and hole transporting properties were found to decrease in the measurement of current density - voltage (CD - V) and capacitance - voltage (C - V) characteristics of Hole Only Devices (HODs) due to thermal damage. At the annealing temperature of 150 °C, the QLEDs device was optimized with TFB films having good hardness and best hole transporting properties for solution processed QLEDs.

We presented enhanced light extraction efficiency of organic light emitting diodes (OLEDs) cells with a nano-sized diffraction grating layer. Various diffraction gratings of different morphologies including linear, cubic, hexagonal and quasiperiodic patterns were fabricated by multiplexing light interference exposure on an azobenzene thin film. The effect of diffraction grating layer on device performances including luminous properties and quantum efficiency was investigated. In contrast to periodic grating patterns, the quasiperiodic structures leading broadband light extraction resulted in improved external quantum efficiency and power efficiency by 73% and 63%, respectively, compared to conventional OLED with flat surface of glass substrate.