Micro-structural effects on the performance of poly(thiophene) field-effect transistors

TitleMicro-structural effects on the performance of poly(thiophene) field-effect transistors
Publication TypeConference Paper
Year of Publication2006
AuthorsA. Salleo, Leslie H. Jimison, Matthew M. Donovan, M.L. Chabinyc, and M.F. Toney
EditorBao, Z, and D.J. Gundlach
Conference NameOrganic Field-Effect Transistors V
Conference Location1000 20TH ST, PO BOX 10, BELLINGHAM, WA 98227-0010 USA
ISBN Number0-8194-6415-5
Keywordsmicro-structure, mobility, poly(thiophene), polymer TFTs
AbstractThe performance of polymer field-effect transistors is highly dependent on their processing history. For instance, thermal processing plays a role in micro-structure development and consequently in device performance. A transport model was developed based on the semiconductor micro-structure where highly mobile states are located in the crystalline areas and defects and disordered regions correspond to areas where carriers are trapped. By applying this model to electrical characterization data of PQT-12 (a regio-regular polythiophene), it is found that annealing tightens the energetic distribution of the traps. Films quenched from the melt performed worse than annealed films due to an increased trap density and broader energy distribution of the traps. X-ray diffraction in grazing and specular geometry was carried out at the Stanford Synchrotron Radiation Laboratory on PQT-12 thin films to reconcile the predictions of the transport model with the micro-structure of the PQT-12 thin films. In all cases the polymer crystallites are textured with the pi-stacking direction in the plane of charge transport and the rocking curves indicate the existence of a population of highly oriented crystallites. Annealing the as-spun films improves the crystallinity and texture, in agreement with the transport model. Quenching produces defects in the films, which are likely to produce traps, thereby lowering the carrier mobility.