양자점으로 구성한 색변환층을 이용하여 제작한 백색 유기발광소자의 특성에 관한 연구

Abstract

White organic light-emitting diodes (WOLEDs) have emerged as excellent candidates due to interest in their potential applications in next-generation full-color displays and light sources. The prospect of promising applications in WOLEDs has led to substantial research and development efforts to enhance their efficiency and color stability. Various studies on the efficiency enhancement of the WOLEDs have been conducted utilizing dual color emitting layers (EMLs), triple color EMLs, color filters, and color conversion layers (CCLs). White light-emitting devices (LEDs) with blue LEDs utilizing CCLs have been suggested due to their excellent advantages of high color stability, high color conversion efficiency, and simple fabrication. WOLEDs with blue LEDs containing CCLs have currently attracted a great deal of interest because of their promising applications in high-efficiency full-color displays and light sources. While phosphor materials have been extensively used as the CCLs of the WOLEDs with high quantum efficiency, inherent problems related to their photometric performance have been still encountered for practical applications in mass production. The significant problems of the phosphor materials used as CCLs in WOLEDs include generation of large emission bandwidth, the inevitable emission tail towards long wavelengths, the difficulty in controlling the granule size, the composition of layers, and the deposition of the uniform films. These disadvantages of the phosphor materials result in the creation of the undesired visible color variations and the complexity in tuning the color properties. Furthermore, the scattering problem of the phosphors, probably due to the large grain size, results in the variation of the color coordinates over angle. Therefore, investigations concerning enhancement of the color stabilization in WOLEDs with CCLs utilizing alternative materials are necessary to enhance device performance. Red and green CdSe/ZnS quantum dots (QDs) instead of phosphor materials have been introduced for the CCL material to achieve the good white stability of the WOLEDs at different applied voltages. The QDs with a narrow emission peak could be effectively excited by a visible light, and the emission peak and intensity of the QDs could be tuned by their size, species, and band alignment. Even though some investigations on electrical characteristics of the WOLEDs utilizing phosphor CCLs have been conducted, very few studies concerning enhancement of the color stabilization in WOLEDs utilizing QD CCL have been performed. This paper reports data for the enhancement of the color stabilization in WOLEDs with a CCL containing core-shell CdSe/ZnS QDs. Photoluminescence (PL) measurements were performed to investigate the optical properties of the QDs. Current density-voltage and electroluminescence (EL) measurements were carried out to investigate the electrical and optical properties of the WOLEDs with QD CCLs.