Enhanced and Anisotropic Charge Transport in Polymer-Based Thin-Film Transistors by Guiding Polymer Growth

Abstract

Ideal molecular features and microstructural properties of organic semiconducting thin films are being explored to achieve high-performance organic thin-film transistors (OTFTs). We prepared and processed hexamethylbenzene (HMB)/poly(3-hexylthiophene) (P3HT) mixtures using a thermal gradient system to fabricate P3HT-based OTFTs. In the thermal gradient system, the HMB separated from the HMB/ P3HT mixtures and crystallized along the sample movement direction. The crystallized HMB affected and guided the growth behavior of P3HT at the molecular level. Observations from joint microscopic and spectroscopic analyses revealed that the HMBprocessed P3HT (H-P3HT) thin film possessed anisotropic and improved microstructures, particularly in crystalline domains. The improved molecular features and microstructural properties of the H-P3HT thin film enhanced the intramolecular and intermolecular charge transport by extending the π-conjugation, decreasing the reorganization energy, and strengthening the π−π overlaps. The electrical performance of the H-P3HT OTFT was augmented significantly with respect to that of the spin-coated P3HT OTFT. In addition, the H-P3HT OTFT exhibited an anisotropic charge transport property, correlating with microstructure directionality and resulting from the difference in the directions of the π−π overlaps. This effective and simple technique can be applied to other device types and has the potential to achieve high-performance organic electronic/photonic devices.

Monte Carlo Simulation for Investigation of Morphology Dependent Charge Transport in Bulk-Heterojunction Organic Solar Cells

“…They have found that the charge mobility is three times higher in the direction parallel to the ordered π-stacks comparing the direction perpendicular to them. The same results have been reported by Wu et al 110 Their results exhibit an improvement in the performance of the field effect transistor in which the direction of most of the (π−π) overlaps was consistent with that of the charge transport from source to drain.…”

Air-Stable Crystalline Polymer-Based Field-Effect Transistors Fabricated by a Thermal Gradient Process

“…After the maximum I DS was achieved, the current of the s-PBTTT-C 14 -based device decayed quickly to 70% of the initial current at 4000 s. In comparison, the current rate of the c-PBTTT-C 14 -based device was still higher than 1 until 4000 s. These results indicate that the crystallized PBTTT-C 14 can effectively reduce the influence of water and oxygen on the device and allow the device to operate stably in an atmospheric environment. This phenomenon was also observed in the crystallized regioregular P3HT as shown in Figure b, in which the electrical characteristics of the P3HT-based OFETs was reported previously . The fabrications of spin-coated P3HT (s-P3HT) and crystalline P3HT (c-P3HT) films are similar to the cases of PBTTT-C 14 .…”

“…This phenomenon was also observed in the crystallized regioregular P3HT as shown in Figure 13b, in which the electrical characteristics of the P3HT-based OFETs was reported previously. 44 The fabrications of spin-coated P3HT (s-P3HT) and crystalline P3HT (c-P3HT) films are similar to the cases of PBTTT-C 14 . What is more special is that the s-P3HT-based OFET crashed during the stability measurement process.…”

Modulating Neuromorphic Behavior of Organic Synaptic Electrolyte-Gated Transistors Through Microstructure Engineering and Potential Applications

“…Figure a shows the normalized absorption spectra of various specimens. The absorption region of P3HT above 540 nm is considered the absorption mainly from crystalline P3HT and below 540 nm reflects the absorption mostly from amorphous P3HT. , The differences in the shape of the absorption peaks of crystalline P3HT among the three types of specimens are small. However, regarding the ratio of amorphous to crystalline absorbance of the P3HT, the DS specimen shows a higher value compared with the ST and SS specimens, suggesting a larger amorphous fraction.…”

“…As plotted in Figure c, the DS and ST specimens have shorter and longer d -spacing values, respectively, indicating that the stacking of P3HT molecules is more compact in the DS specimen and is looser in the ST specimen. The crystalline size ( L cry ) of different P3HT specimens can be estimated using the Scherrer equation: , L cry = K λ β ⁡ cos ⁡ θ where K is the Scherrer constant and a value of 0.9 is used, , λ is the wavelength of X-ray, β is the half-width of a diffraction peak, and θ is the position of a diffraction peak. As shown in Figure c, the DS specimen has a larger L cry than the other two kinds of specimens.…”