Doping Effects on Organic Interfaces

Organic electronics are an integral area of research because organic semiconductors can be lightweight, flexible, and biodegradable with low-cost production methods such as ink-jet or roll-to-roll printing. These inexpensive mass production techniques require solution deposition of the organic material. While single crystal organic semiconductors have been shown to exhibit carrier mobilities comparable to the silicon currently used in photovoltaics, during solution deposition of common organic semiconducting materials the resultant thin-film is often polycrystalline. Device performance and electrical properties of organic thin-film transistors are highly dependent on crystal structure and molecular packing. In polycrystalline thin-films, boundary regions between crystal grains can affect the overall performance of devices, as crystal structure and packing may differ from that of the surrounding crystal regions. These boundary regions may also serve as defect sites, allowing environmental factors, such as oxygen content and humidity, to alter local charge transport through devices. We utilize Kelvin Probe Force Microscopy (KPFM) to characterize how grain boundaries alter local conductivity and device performance as a function of doping in 2,8-difluoro-5,11-triethysilylethynyl anthradithiophene (diF TESADT) thin-film transistor surfaces. Device voltage drops at grain boundaries are characterized as a function of both atmospheric dopants and transition time between dopants.