Theory and simulation of amorphous organic electronic devices

Abstract

The electronic properties of amorphous organic thin films are of great interest due to their application in devices such as light emitting devices, solar cells, photodetectors, and lasers. Compared to conventional inorganic semiconductors, amorphous organic thin films have the potential to enable entirely new functionality, larger areas, higher efficiencies, flexible substrates, and inexpensive fabrication. The development of amorphous organic electronic devices requires a deep understanding of the physics of the underlying electronic processes, which are controlled by the behavior of polarons (charged molecular states), and excitons (neutral molecular excited states). In this thesis we employ microscopic models of polaron and exciton processes to calculate macroscale phenomena in amorphous small molecular weight organic thin films using Monte Carlo (MC) simulations. The principle results that we report are: (1) the experimental demonstration and theoretical analysis of the previously neglected phenomenon of solid state solvation; (2) the identification of significant errors in existing models of molecular energy level disorder in polarizible media;

(cont.) (3) the most rigorously self-consistent quantitative fit of a dispersive exciton diffusion model to experimental data from a small molecular weight amorphous organic solid; (4) MC simulations of equilibrium polaron mobilities in amorophous organic solids as a function of both field and carrier concentration; and (5) MC simulations of space charge limited (SCL) currents through thin films as a function of voltage under typical operating device conditions. To our knowledge, the simulations of polaron transport reported here represent the most accurate calculations of equilibrium mobilities and SCL currents based on modern models of polaron transport in disordered molecular solids.