Challenges in Doping of Organics: Small Molecules vs. Polymers

Controlling the charge carrier densities is a key feature of any semiconductor electronic device. In inorganic semiconductors, general understanding of doping has been achieved early on and research has concentrated on finding dopants in large-gap systems like nitrides. In organic materials, doping is now a routine technique for mass-produced OLED displays and organic solar cells. However, it is still far from a microscopic understanding. Furthermore, doping in organic systems where both electronic and ionic transport happen has recently generated much interest.<br/>In this talk, I will address these two very different systems: I will discuss recent progress in understanding the doping in small-molecule semiconductors, touching new dopants and high mobility materials, allowing to realize devices like the first organic bipolar transistors.<br/>I will compare to recent work on the doping of organic electrochemical transistors (OECTs). These devices have recently been investigated broadly since they offer switching and sensing functionality in an electrolytic environment compatible with biological systems. The mixed electron-ion transport of the devices has consequences for the doping process, making it significantly different from the electrostatic doping of standard FET devices.