We developed methods of combining semiconductor quantum dots (QDs) and organic and inorganic metal oxides in solution–processed light–emitting devices (LEDs). Several distinct QLED structures fabricated with many types of QDs were studied. In addition to controlling the concentrations of holes and electrons within a multilayered device, which determines the luminance and efficiency of QLEDs, using metal oxide layers is advantageous for fabricating QLEDs showing long–term stability because metal oxides are stable in air and prevent the water vapor and oxygen in the ambient air from permeating into the QD–emission layer. Moreover, the wet–chemistry processing required for manufacturing QLEDs makes metal oxide layers attractive for manufacturing QLEDs at low cost and/or on a large scale. As processing methods of QDs depend on the properties of surface groups consisting of the organic–capping ligand surrounding the QDs, these surface groups must also be treated to form close–packed, highly conducting QD layers in order to improve device efficiency. Several QD and structure types enable us to fabricate QLEDs showing various colors and efficiencies for various technological applications. In addition, we developed various methods of fabricating patterned structures that can be integrated into QLEDs to improve light outcoupling efficiency.
We determined the physical operation of the QLEDs by performing electrical and optical measurements and morphological analysis, which further provides fundamental physical understanding of the interactions among inorganic, organic, and QD semiconductors and of design and selection of material for QLEDs.
