High-performance organic semiconductors: understanding charge carrier and exciton dynamics

Organic semiconductors have attracted considerable attention due to low cost, easy fabrication, and tunable properties. A number of applications based on organic semiconductors (that include organic light-emitting diodes and thin-film transistors) are already on the market, and recent developments in the field, which I will review, promise more to come. Of special technological interest are solution-processable materials that can be cast into thin films. In this presentation, I will discuss fluorescent and photoconductive properties of solution-deposited organic thin films and how these properties can be manipulated by changing molecular packing and introducing guest molecules. In particular, photocurrent enhancement and different charge carrier dynamics can be achieved, depending on the guest molecule, due to various outcomes of competition between photoinduced charge and energy transfer between host and guest molecules. I will summarize the results of our comprehensive studies of these properties using time-resolved fluorescence and photoconductivity (from ~100 ps to seconds after photoexcitation) techniques to probe the processes responsible. I will also discuss properties of our molecules on a single-molecule level measured using single-molecule fluorescence spectroscopy.