Low-Voltage Organic Transistors Based on Tetraceno[2,3-b]thiophene: Contact Resistance and Air Stability

The small-molecule organic semiconductor tetraceno[2,3- b ]thiophene has been synthesized through an environmentally friendly synthetic route, utilizing NaBH 4, rather than Al/HgCl 2, for the reduction of the quinone. Low-voltage organic thin-film transistors (TFTs) have been fabricated using tetraceno[2,3- b ]thiophene and, for comparison, pentacene and anthradithiophene as the semiconductor. The tetraceno[2,3- b ]thiophene TFTs have an effective field-effect mobility as large as 0.55 cm 2 V –1 s –1 and a subthreshold swing of 0.13 V/decade. In addition, it has been found that the contact resistance of the tetraceno[2,3- b ]thiophene TFTs is substantially smaller than that of the anthradithiophene TFTs and similar to that of the pentacene TFTs. The long-term air stability of TFTs based on all three semiconductors has been monitored over a period of 12 months. The initial charge-carrier mobility of the tetraceno[2,3- b ]thiophene TFTs is ∼50% smaller than that of the pentacene TFTs, but as a result of the greater ionization potential and better air stability induced by the terminal thiophene ring condensed at the thiophene- b -bond, the tetraceno[2,3- b ]thiophene TFTs outperform the pentacene TFTs after continuous exposure to ambient air for just 3 months.