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 (Vth) and operate both as accumulation- and depletion-mode transistors. Hence, the BS phenomenon was analyzed by recording the IDS(t) time curves when the devices were driven under both negative and positive gate-source voltages (VGS). The BS measurements performed in this work confirm the conventional decay of the IDS(t) when positive VGS values (charge accumulation regime) are applied. On the other hand, IDS(t) increases very rapidly when the devices are polarized with negative VGS (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. O2 and H2O) as origin of the BS phenomenon in these n-type field-effect transistors.