Structure of Pentacene Monolayers on Amorphous Silicon Oxide and Relation to Charge Transport

Organic semiconductors are attracting considerable research interest due to already commercialized and potential applications in low-cost electronics such as organic light emitting diode (OLED) displays, thin film transistors and related applications (e.g. TFT sensors), RF identification tags (RFID), smart cards electronic paper etc.). In the field of organic semiconductor research, the material pentacene has developed into a benchmark material because high-performance thin film transistor (TFT) devices are easily and robustly obtained from vacuum-deposited thin films of pentacene on a variety of substrates. Pentacene thin films on silicon oxide are a particularly interesting case because, despite their polycrystalline film morphology (i.e. structural imperfections and small grains), the pentacene TFTs outperform single crystalbased pentacene transistors. The key to understanding the electrical performance of pentacene TFTs lies with the first few layers of pentacene. When a TFT device is switched “on”, the current flows predominantly in the first few molecular layers and the packing and exact arrangement of molecules in these layers determine the current obtained at an applied voltage. The knowledge of the precise packing in the first monolayer is, therefore, crucial to understanding the charge transport properties of pentacene TFTs.