양자점을 포함한 활성층을 가진 유기발광다이오드의 전기적 광학적 특성에 관한 연구

Abstract

Organic light-emitting devices (OLEDs) have emerged as potential candidates for various applications in promising full-color displays and white lighting sources, which offer excellent advantages of low power consumption, high contrast ratio, wide viewing angle, fast response speed, and ultra-thin thickness. Solution-based OLEDs have several advantages of simpler fabrication and lower cost in comparison with evaporation-based OLEDs. However, solution-based OLEDs have inherent problems of low-stability, low lifespan, high oxidation, and poor color balance. Several kinds of methods for the fabrication of high-efficiency OLEDs by using a solution process have been suggested to overcome the inherent problems, and various alternative methods for fabricating solution-based have been introduced to achieve color purity and color tunability by utilizing quantum dots (QDs). Even though some studies concerning OLEDs fabricated utilizing hybrid inorganic/organic nanocomposites containing semiconductor QDs have been performed to enhance their efficiency and color stabilization, investigations on the fabrication and the device characteristics of OLEDs with CdSe/CdS/ZnS core/shell/shell QDs embedded in small molecules have yet to be performed. Thus, systematic studies of the electrical and the optical properties of OLEDs fabricated utilizing small molecules containing CdSe/CdS/ZnS core/shell/shell QDs are necessary if their efficiency and their color stability are to be improved. This paper reports the electrical and the optical properties of OLEDs with a small molecular active layer containing CdSe/CdS/ZnS core/shell/shell QDs. OLEDs with a 1,3-bis(9-carbazolyl)benzene (mCP) or a (9-(3-(9H-carbazol-9-yl)phenyl)-9H-carbazol-3-yl)-diphenylphosphine oxide (mCPPO1) layer containing CdSe/CdS/ZnS quantum dots (QDs) were fabricated. The photoluminescence spectrum for the QDs showed a dominant exciton peak. Measurements of the current density as a function of the voltage showed that the turn-on voltage of the OLED with an mCP layer containing QDs was as small as 5 V, and measurements of the luminance as a function of the voltage showed that the luminance of the OLED with an mCP layer containing QDs was much larger than that of the OLED with an mCPPO1 layer containing QDs. Electroluminescence spectra for OLEDs with an mCP layer containing QDs showed that the dominant exciton peaks corresponding to the QDs were located at almost the same positions, regardless of the applied voltage.