Mechanically Stable Flexible Organic Field Effect Transistors (OFETs)

Abstract

Flexible organic field-effect transistors with high mechanical stability are fabricated on indium tin oxide coated polyethylene terephthalate substrates with TIPS-Pentacene semiconductor crystals formed by drop casting on a hybrid gate dielectric consisting high-k hafnium dioxide grown by atomic layer deposition and poly(4-vinylphenol) deposited by spin coating. Devices with TIPS-Pentacene crystallites exhibited excellent p-channel characteristics with field-effect mobility values up to 0.12 cm2/Vs, high current on/off ratio >104, and low threshold voltage of -0.2 V at -15 V operations. Device performance was slightly affected by mechanical strain applied by bending with radius varying from 12.5 mm to as low as 5.0 mm, primarily due to the changes in dielectric morphology upon strain application as confirmed by atomic force microscopy of dielectric surface. High stability in device performance was demonstrated upon applying constant tensile strain with low bending radius of 5.0 mm for more than 48 hours. Further in order to improvise the performance of the devices flexible TIPS-pentacene:PVP bi-layer organic field-effect transistors (OFETs) have been fabricated with optimizing different parameters to achieve high electrical stability under effects of mechanical strain and bias stress. The new fabricated devices were found to have ?sat 0.14(0.10) cm2 V-1 s-1 with ?max of 0.3 cm2 V-1 s-1 at -10 V operations and high Ion/Ioff of order of 105 was achieved for these devices, which is one order higher as compared to batch 1 devices. In addition no significant change in device performance is observed even after 5 days of continuous bending at a fix Rbend of 5 mm.