Byung Min Park

Preparation and Characterization of White Polymer Light Emitting Diodes Using PVK:PFO:MDMO-PPV Emission Layer

White polymer light emitting diodes (WPLEDs) with a glass/ITO/PEDOT:PSS/PVK: PFO:MDMO-PPV/TPBI/LiF/Al structure were fabricated to investigate the effects of the doping concentration of MDMO-PPV emission materials. The PVK, PFO and MDMO-PPV conjugated polymers as host and guest emission materials were spin coated at various concentrations of MDMO-PPV ranging from 15.0 to 30.0 vol%. As the concentration of MDMO-PPV increased from 15.0 to 30.0 vol%, the luminance and current efficiency values were decreased clearly, which are attributable to the quenching effect at a high doping concentration. The maximum luminance and current efficiency were 2280 cd/m2 and 3.83 cd/A, respectively for a WPLED with 15.0 vol% of MDMO-PPV. The average CIE color coordinates were about x = 0.33, y = 0.37 at 15 V, showing a white emission color.

Preparation and properties of passivation film layers spray coated flexible Cu(In, Ga)Se 2 solar cells

Recently, the flexible thin film solar cells such as the organic solar cells and Cu(In, Ga)Se2 (CIGS) solar cells have been attracting much attention as the photovoltaic devices, because it has many advantages such as simple process with a light weight, and its flexible large area applications. In addition, solar cells as an energy source can be applicable to the unmanned aerial vehicle (UAV) and IoT system, which is the interconnection of identifiable objects through the wireless internet systems. In order to improve the reliability of the devices, it is desirable to optimize the passivation materials and structures. The passivation treatment is a key technology in order to prevent the devices from atmospheric oxygen and moisture. As one of the methods to commercialize the flexible solar cells, hybrid type encapsulation films using organic and inorganic materials can be effective in blocking the penetration of water and oxygen into the devices.

Preparation and characterization of organic light emitting devices using hybrid encapsulation materials properties of OLED using hybrid encapuslaton materials

Many researchers have been focusing on the development of the new energy saving devices. The optoelectronic devices such as organic solar cells (OSCs) and organic light emitting diodes (OLEDs) have been regarded as the next generation energy saving devices. In addition, those devices can also be applied to the Internet of Things (IoT), which is the interconnection of identifiable objects through the wireless internet systems. In addition, IoT is expected to provide advanced connectivity of the devices, systems, and services. In this study, for future applications of smart farm and buildings, the flexible OLEDs were prepared by the spin coating and thermal evaporation methods. The stability of the devices by introducing of the hybrid encapsulation materials using organic and inorganic passivation materials were investigated. The lifetime of the devices are affected by the humidity and oxygen environment. Therefore, encapsulations using hybrid inorganic and organic materials of the devices would be important technologies in order to prevent the devices from the oxygen and moisture. As a result, the prepared OLED device with the hybrid encapsulation materials showed better stability and reliability compared with glass capped OLED devices.

Properties of Bulk Heterojunction Organic Solar Cells with LiF Buffer Layer at Various Concentrations of Active Layer

We fabricated organic solar cells (OSCs) using poly[2,6(4,4’bis(ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-alt-(1,3-(5-octyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione))] (PD-TSTPD) and (6,6)-phenyl-C71 butyric acid methyl ester (PC71BM) active materials. PDTSTPD and PC71BM solutions for the active layer were mixed at concentration ratios of 1:1, 1:2, 1:3, and 1:4 wt%, respectively. The effects of OSCs at various concentrations of active layer on the electrical and morphological properties of the device were investigated. The performance of the OSC at a concentration ratio of 1:3 wt% showed the best electrical properties among the prepared samples, indicating that the maximum short circuit current density (Jsc), open circuit voltage (Voc) and power conversion efficiency (PCE) values were about 6.9 mA/cm2, 0.849 V and 2.3%, respectively. PDTSTPD:PC71BM active layer with a concentration ratio of 1:3 wt% showed smooth film roughness compared to the other prepared samples, which may lead to an improvement of the electron injection efficiency into the cathode electrode.

Fabrication and Characterization of White Phosphorescent Polymer Light Emitting Diodes Using PVK:FCNIrpic:Ir(mppy)3:Ir(piq)3

White phosphorescent polymer light emitting diodes (WPhPLEDs) with a glass/ITO/ PEDOT:PSS/PVK:FCNIrpic:Ir(mppy)3:Ir(piq)3/TPBI/LiF/Al structure were fabricated to investigate the effects of the doping concentration of Ir(piq)3 emission materials. The PVK, FCNIrpic, Ir(mppy)3 and Ir(piq)3 organic materials as the host and guest emission materials were spin coated at various concentrations of Ir(piq)3 ranging from 0.1 to 0.4 wt%. With increasing the concentration of Ir(piq)3 from 0.1 to 0.3 wt%, the luminance was increased clearly. However, the luminance was decreased by 6400 cd/m2 when the Ir(piq)3 doping concentration reached 0.4 wt%. The drop in luminance is caused by the quenching effect at a high doping concentration. The maximum luminance and current efficiency were 9486 cd/m2 and 2.23 cd/A, respectively for WPhPLED with 0.3 wt% of Ir(piq)3. The average CIE color coordinates for the WPhPLED with 0.2 wt% of Ir(piq)3 were about (x=0.32, y=0.33) at 12V, showing a good white emission color.