Effect of Mesoscale Crystalline Structure on the Field-Effect Mobility of Regioregular Poly(3-hexyl thiophene) in Thin-Film Transistors

Abstract

Regioregular poly(3‐hexyl thiophene) (RR P3HT) is drop‐cast to fabricate field‐effect transistor (FET) devices from different solvents with different boiling points and solubilities for RR P3HT, such as methylene chloride, toluene, tetrahydrofuran, and chloroform. A Petri dish is used to cover the solution, and it takes less than 30 min for the solvents to evaporate at room temperature. The mesoscale crystalline morphology of RR P3HT thin films can be manipulated from well‐dispersed nanofibrils to well‐developed spherulites by changing solution processing conditions. The morphological correlation with the charge‐carrier mobility in RR P3HT thin‐film transistor (TFT) devices is investigated. The TFT devices show charge‐carrier mobilities in the range of 10–4 ∼ 10–2 cm2 V–1 s–1 depending on the solvent used, although grazing‐incidence X‐ray diffraction (GIXD) reveals that all films develop the same π–π‐stacking orientation, where the <100>‐axis is normal to the polymer films. By combining results from atomic force microscopy (AFM) and GIXD, it is found that the morphological connectivity of crystalline nanofibrils and the <100>‐axis orientation distribution of the π–π‐stacking plane with respect to the film normal play important roles on the charge‐carrier mobility of RR P3HT for TFT applications.

Molds and Resists Studies for Nanoimprint Lithography of Electrodes in Low-Voltage Polymer Thin-Film Transistors

“…24 The latter is a result of the Poole-Frenkel effect, which is generated by an increase on the planar electric field from source to drain. Charge carrier mobility in these TFTs are comparable to previously reported results, 10,11,25 but the low operating voltage indicates a possibility to function in aqueous media for sensing applications such as medical diagnosis and beverage evaluation by electronic tongues. 8,9 Furthermore, TFTs with microimprinted electrodes may operate at higher frequencies, due to reduced L and higher l, which is necessary for producing potentially competitive low-cost polymeric devices.…”

“…The patterning procedure was demonstrated for poly(3-hexylthiophene) (P3HT) transistors, as this is a well-known polymeric semiconductor with several reports in the literature, being already applicable for gas sensing. 8,9 Even though charge carrier mobility in these p-type polythiophene derivatives approaches amorphous silicon, 10,11 it requires high dielectric constants (j) to make it suitable for electronic applications. As already demonstrated by our group, P3HT on titanium oxynitride (TiO x N y ) can provide low-voltage hybrid TFTs but demands shorter channel length to achieve higher frequency operation.…”

Molecular-weight dependence of interchain polaron delocalization and exciton bandwidth in high-mobility conjugated polymers

“…8 On a mesoscopic scale P3HT can be made to adopt well defined nanoribbons using various processing techniques. [9][10][11] The mobility depends critically on manifold other factors such as molecular weight, interaction between polymer and solvent, and deposition conditions. 12 Recent research by McGehee et al 13,14 and Neher et al, 15 focusing on the effects of molecular weight ͑MW͒, has shown that MW is another dominant factor to affect mobilities by several orders of magnitude in a regime with mobilities less than 10 −2 cm 2 / V s. They found that the mobility increases with MW in spite of reduced crystallinity at higher MW, indicating that charge transport depends on factors other than the degree of crystallinity.…”

Template-mediated nano-crystallite networks in semiconducting polymers

“…Therefore, we speculate that the TMC-induced fibrillar network nanostructure Structural evolution and 3D electrical percolation network. To investigate the improved structural orientation of the P3HT:PSS films, we performed grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements [30][31][32] on the P3HT and P3HT:PSS films (see Methods for further details). Figure 2a,b present twodimensional GIWAXS profiles of the pristine P3HT and the P3HT:PSS films.…”