Organic thin-film transistors with flame-annealed contacts

Reducing contact resistance is critical to developing high-performance organic field-effect transistors (OFETs) since it impacts both the device mobility and switching speed. Charge injection and collection has been optimized by applying chemical treatments to the contacts, such as self-assembled monolayers (SAMs), oxide interlayers, or dopants. Here, we tested how flame annealing the surface of the electrodes impacts the interface and bulk components of the contact resistance, as well as the overall device performance. A butane micro torch was used to flash-anneal the gold electrodes, which allowed gold grains to crystallize into larger domains. We found that, along with the grain size, the surface roughness of the contacts was also increased. SAM treatment created a lower work function shift on a flame annealed electrode than when deposited on an untreated surface, due to the greater surface roughness. This resulted in a larger interface contact resistance. However, flame annealing also produced an order of magnitude reduction in the density of trap states in the semiconductor layer, which reduced the bulk contact resistance and channel resistance. These competing effects yielded OFETs with similar performance as untreated devices.