Laser printing of air-stable high performing organic thin film transistors

Abstract

Active layers involved in top contact organic thin film transistors (TC-OTFTs) have been printed using the laser induced forward transfer (LIFT) technique. Bis(2-phenylethynyl) end-substituted terthiophene (diPhAc-3T) as a p-type organic semiconductor was vacuum evaporated on a quartz substrate prior to the transfer by laser onto an acceptor substrate to form an organic active layer for charge transport. The resulting printed diPhAc-3T pixels on the receiver substrates have a homogeneous morphology as shown by optical microscopy and atomic force microscopy (AFM). Electrical characterizations demonstrated that these transistors are fully functional with hole mobilities up to 0.04cm2/Vs, threshold voltage Vt near 0V and Ion/Ioff ratio up to 2.8×105. The efficient cohesion of diPhAc-3T vacuum evaporated thin films induced by 3-dimensional growth offers an exceptionally high physical resistance to laser pulses. The large intermolecular interaction involved in such growth mechanism makes the thin films less sensitive to the mechanical damages induced by the laser. Due to the optical properties of diPhAc-3T, the use of a protecting layer deposited on the donor substrate prior to the diPhAc-3T active layer to trap the incident radiation during the LIFT was not required.