Transport property and charge trap comparison for N-channel perylene diimide transistors with different air-stability

N-type organic field-effect transistors (OFETs), based on two perylene diimide semiconductors (PDI-8 and PDI-8CN₂) exhibiting very different air sensitivities, have been fabricated on Si/SiO₂ substrates. These OFETs have been electrically characterized in vacuum both in the dark and under white-light illumination by dc transfer and output curves, bias stress experiments and variable temperature measurements. In particular, the combination of variable temperature and light illumination experiments is shown to be a powerful tool to clarify the influence of charge trapping on the device operation. Even if, in vacuum, the air-sensitive PDI-8 devices display slightly better performances in terms of field-effect mobility and maximum current values, according to our results, charge transport in PDI-8 films is much more affected by charge trap states compared to PDI8-CN₂ devices. These trapping centers are mainly active above 180 K, and their physical nature can be basically ascribed to the interaction between silanol groups and water molecules absorbed on SiO₂ surface that is more active above the H₂O supercooled transition temperature.