Electronic Traps Induced by Radiation in Organic Field-Effect Transistors

Organic field-effect transistors (OFETs) have a range of attractive properties that make them a compelling and advantageous solution in the field of electronics. These properties include the ability to solution process the constituent layers, tune molecular structure to adjust their electronic characteristics, and make flexible, biocompatible devices, all at a competitive cost. One possible application of OFETs is in radiation dosimetry, since radiation dosimeters based on OFETs (RAD-OFETs) offer the possibility of creating inexpensive, flexible devices to accurately measure radiation doses with a response similar to that of human tissue. This can enable better patient care in medical applications such as cancer treatments and improved safety in environments with increased levels of radiation.<br/><br/>Here we present our findings on the nature of electronic traps induced within the organic semiconductor when integrated in RAD-OFETs. These devices were exposed to 6 MeV X-ray radiation. produced by a clinical linear accelerator, with dosages ranging from 0 Gy to 5 Gy. RAD-OFETs based 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (dif-TES-ADT) were fabricated and characterized via IV measurements, photoluminescence spectroscopy, and grazing-incidence wide-angle X-ray scattering (GIWAXS). Compared to control devices, the samples exposed to a 5 Gy dose of radiation exhibited a large shift in threshold voltage and change in subthreshold slope indicating a difference of interfacial trap density of 9×12 eV^-1 cm^-2. A spectral analysis of the trap density of states was also performed utilizing the Grünewald method. We observed that devices exposed to radiation had an increase in the density of trap states by 3×10¹⁷ cm⁻³, while no change was detected for the control devices. Photoluminescence spectroscopy measurements of the ratio of intensities for the 0-0 and 0-1 transitions demonstrated a change in activation energy from 56 meV to 71 meV, evidence that radiation exposure increases local structural disorder within the aggregates. GIWAXS analysis also confirmed structural disorder as a cause for the increase in trap states with the growth of a second peak in the main reflection for samples exposed to radiation. Our results provide a deeper understanding of radiation-induced defects in organic semiconductors, which can inform the creation of more efficient and reliable radiation dosimeters.