Sunjin Song

Paper as a Substrate for Inorganic Powder Electroluminescence Devices

Alternating-current-type inorganic powder electroluminescence (PEL) devices were successfully fabricated on four kinds of paper substrates, i.e., glossy paper, sticker paper, magazine paper, and newspaper. To protect the paper from wet chemical and heating processes during the formation of the PEL device, the paper substrate was coated with a spin-on-glass layer that served as a buffer layer. In spite of the fragility of paper, quite satisfactory results were obtained-the performance of paper-based PEL devices was almost equivalent to that of PEL devices on a plastic substrate. Extension of a substrate to paper, even to flimsy daily newspaper, will widen the opportunity of PEL devices as one of flexible and disposable displays.

A chlorinated barium titanate-filled polymer composite with a high dielectric constant and its application to electroluminescent devices

We have studied the effect of chlorination on the dielectric performance of a barium titanate (BTO)–polymer film. Functionalization of BTO powder particles with chlorine (Cl) atoms and/or Cl-containing functional groups was achieved by a simple treatment using chlorinated solvents. The chlorinated BTO (Cl-BTO) particles were incorporated into a cyanoethyl-based polymer and the mixture was spin-coated to produce a composite film. The dielectric constant of the composite film with Cl-BTO was as high as 208 at a frequency of 10 Hz, showing a 2.5-fold increase in dielectric constant compared to composites composed of the neat BTO and the cyanoethyl-based polymer at a frequency of 10 Hz. The observed dramatic increase in dielectric constant would be caused by the interfacial polarization due to the p-type doping effect resulting from the presence of strong electronegative Cl atoms. Given a relatively high dielectric constant, composite films with Cl-BTO were further exploited as a dielectric layer in an inorganic electroluminescence (EL) device. The luminance of the EL device with Cl-BTO was 4090 cd m−2 at a frequency of 1 kHz, showing a 2.03-fold increase in luminance compared to that with the untreated BTO. The improved performance of the EL device is attributed to a high dielectric constant of the composite films that allow for efficient charge carrier tunneling into the phosphor and therefore enhanced luminance and efficiency.

Field-Enhancement Effect of Short Carbon Nanotubes Using an Electrical Aging Treatment on Inorganic Electroluminescence

AC inorganic electroluminescence (EL) devices were fabricated using the emitting layer composed of phosphor-single-walled carbon nanotubes (SWCNTs) composite (PSC) to utilize the local field enhancement of SWCNTs. In order to enhance the electric field in an emitting layer with minimized current paths, bare long SWCNTs were shortened by cryogenic crushing method. After electrical aging treatment of the PSC device, partly formed short SWCNT networks in the emitting layer were effectively removed during the electrical aging treatment. High performance of 60% and 43% increase in efficiency and luminance, respectively, was achieved. This PSC device with short SWCNTs could lead to high brightness due to increased electron tunneling into phosphor. The PSC device reveals the importance of high electric field by SWCNTs leading to high EL performance.

Enhanced Optical and Electrical Properties of Inorganic Electroluminescent Devices Using the Top-Emission Structure

Alternating current inorganic powder electroluminescence (EL) devices with a top-emission structure were fabricated on glass substrates to investigate the structural dependence on EL. The EL performance was examined by comparing the top-emission structure with the conventional EL device, i.e., the bottom-emission structure. High performance, such as 50 and 40% increases in efficiency and brightness, respectively, was achieved. This enhanced EL performance was attributed to the structural change in the EL device, leading to reduced optical loss and enhanced electric field applied to the phosphor.