Abstract
This thesis studies various aspects of electron injection into organic light-emitting diodes (OLEDs) using density functional theory and the master equation approach (only the last chapter). The first part of the thesis studies the relation between the work function and the surface stability of a multitude of compounds (Ca2N, BaAl4, CaAl4, BaAuIn3, LaB6 and CrO2) having different crystal structures and consisting of elements from various parts of the periodic table. The work function and surface stability are materials properties that are crucial for cathodes, used in many devices ranging from microwave ovens to OLEDs. The common perception, however, was that stability and a low work function are incompatible in general. From the studies, a general model is constructed for metallic compounds, including the transition-metal oxides that predicts large anisotropies and stable low-work-function surfaces for many metals with polar surfaces. Chapter seven studies the ground state of the fifth element. Boron is a technologically interesting material, and challenging for both experimentalists and theoreticians. The most stable ß rhombohedral structure found exhibits an electronic structure consistent with known experiments when impurities add two electrons. The inclusion of zero point energies turns this structure into the ground state of elemental boron, also at finite temperatures. Chapter eight studies the spin-orbit coupling (SO) in lead-telluride and graphite. For PbTe the wavefunction character at the Fermi level is determined and for graphite the Landé g-factor is calculated, which compares quite reasonably to experiment. The final chapter simulates electron injection into disordered organic semiconductors for both Ohmic” and Schottky” contacts. It is concluded that an advanced continuum description fails for devices far from equilibrium, that disorder decreases the differences between the two contact types and increases the overall charge density
