The dependence of electrical performance on structural organization in low mobility polymer field effect transistors
Emily G. Bittle, Hyun W. Ro, Chad R. Snyder, Sebastian Engmann, Regis J. Kline, Oana Jurchescu, Dean M. DeLongchamp, David J. Gundlach
Polymer semiconductors are contenders for use in printed, flexible electronics. Though organic electronic materials have been studied for many years, the physics of charge transport is still under investigation. This is in part due to the large variability in transport behavior owing to the large variety of molecules and polymers that can be synthesized, as well as variability in electrical characterization due to device and processing variability. Molecular ordering in organic semiconductors is known to alter the transport characteristics of transistors, and attention to long range and short range ordering provides clues as to the nature of charge transport pathways in the material. Here we study a set of three incrementally ordered regioregular poly(3-hexylthiophene, 2,5-diyl) films in order to track the changes in the final device characteristics. Samples were carefully prepared in order to obtain a set of three films with incrementally increasing order on a set of identical transistor architectures. Ordering was characterized using a variety of short and long range techniques in order to probe the coherence and number of crystallites formed during processing, and the correlation or lack of correlation between these different measures of order were quantified. We observe three changes in transistor characterization with ordering that show a shift from non-ideal to more textbook- like characteristics of the transistor with increasing order: reduction of the contact resistance, a gradual shift to field independent mobility, and a shift from a diode-like (S- shaped) response to linear at low lateral fields.