Bias stress effects investigated in charge depletion and accumulation regimes for inkjet-printed perylene diimide organic transistors

In the present work, we investigated the bias stress (BS) effect taking place in inkjet-printed n-type N,N'-bis(n-octyl)-1,6-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI8-CN2) transistors fabricated on SiO2 gate dielectric. PDI8-CN2 films were deposited from solvent systems able to improve the layer structural uniformity. These devices were found to exhibit largely negative threshold voltages (V-th) and operate both as accumulation- and depletion-mode transistors. Hence, the BS phenomenon was analyzed by recording the I-DS(t) time curves when the devices were driven under both negative and positive gate-source voltages (V-GS). The BS measurements performed in this work confirm the conventional decay of the I-DS(t) when positive V-GS values (charge accumulation regime) are applied. On the other hand, I-DS(t) increases very rapidly when the devices are polarized with negative V-GS (charge depletion regime). The data achieved for the inkjet-printed devices were also compared with those measured under the same stressing conditions for a device fabricated by evaporating PDI8-CN2 on the same SiO2 substrate type. All the experimental observations reported in this work support the validity of a recently-proposed model, prompting for the occurrence of electrochemical reactions involving PDI8-CN2 molecules and ambient agents (i.e. O-2 and H2O) as origin of the BS phenomenon in these n-type field-effect transistors. (C) 2013 Elsevier B.V. All rights reserved.