ABSTRACT
The contributions included in this book underscore the importance of the structural, chemical, and electronic properties of interfaces in organic devices. The progress made in the past decade in developing new multicolor organic light-emitting diodes (OLEDs) [1-7], optically and electrically pumped lasers [8,9], thin-film transistors [10-13], and solar cells [14,15] is advancing the field of organic polymers and small molecule materials at an astounding pace. The vast majority of these devices have a thin-film architecture, which comprises multiple organic-inorganic and organic-organic interfaces [1-7]. Because of the very nature of thin-film devices, these interfaces are generally located within a few molecular planes from active regions. Their electronic and chemical properties determine the characteristics of charge carrier injection into and transport through the device. OLEDs require that injection of electrons and holes be balanced in order to maximize device quantum efficiency (Figure 1). The injection of these charge carriers must be efficient and stable under operation. Metal-organic contacts undergo complex and spatially extended chemical interactions, which can dominate the electrical properties of interfaces. Organic-organic heterojunctions in OLEDs control the transport of carriers between layers
Electron-transport emissive layer
Hole-transport layer
Low work function cathode
LUMO
Transparent high work function anode
Figure 1 Schematic energy diagram of a heterojunction OLED under bias. Electrons (holes) are injected from a low (high) work function cathode (anode) into the electron (hole) transport layer. The heterojunction is designed here to favor exciton formation and radiative recombination in the electron transport layer.
