Organic light-emitting diode (OLED) technology is emerging as a leading next-generation technology for electronic displays and lighting. Rapid advance in OLED application demands in advanced OLED structures. Stacked OLED (SOLED) architecture in which multiple emissive units are vertically stacked is a promising candidate. It can not only be utilized in full-color display with high fill-factor and high resolution but also be used as high efficiency lighting device providing enhanced light output without increasing the driving current. This thesis discusses the design and fabrication of SOLED with metallic intermediate electrodes....[ Read more ]

Organic light-emitting diode (OLED) technology is emerging as a leading next-generation technology for electronic displays and lighting. Rapid advance in OLED application demands in advanced OLED structures. Stacked OLED (SOLED) architecture in which multiple emissive units are vertically stacked is a promising candidate. It can not only be utilized in full-color display with high fill-factor and high resolution but also be used as high efficiency lighting device providing enhanced light output without increasing the driving current. This thesis discusses the design and fabrication of SOLED with metallic intermediate electrodes.

We demonstrate that metallic layers consisting of Ca/Ag, Al/Au, and Al/Ag can be introduced in the fabrication of high efficiency and novel structure two-unit SOLED as the efficient intermediate electrodes. This is possible when treating the surface of Ag or Au with appropriate CF₄-plasma in the course of fabrication to enhance its hole injection ability. The two-unit single color SOLED with semitransparent Ca/Ag or Al/Au has been successfully characterized of double luminous efficiency compared to the conventional single unit device. We use such efficient metallic layers to connect individual red and blue emissive units in one stack in order for mixing them as white light. This SOLED can be totally biased to produce white light emission as well as individually biased to achieve any combination of two colors.

We also develop another kind of SOLED implementation using a reflective composite silver electrode as the intermediate layers; the light emission can thus go double-side. With this reflective bipolar intermediate electrode, both bottom- and top-emission are characterized with high efficiency.

The layered structure of SOLED with metallic intermediate electrodes give rise to microcavity resonance which will incur enhancement of light output if properly designed. A classical model of microcavity effect has been used to analyze and design our two-unit SOLED in pursuit of high efficiency.

As a demonstration, we have successfully fabricated a high-efficiency two-unit SOLED with optimum thicknesses configuration derived from above optical modeling. Such SOLED shows more than twice the efficiency of the reference single-unit device. Experimental results agree well with theoretical prediction.