Electrical Signature of Ultrasound-Induced Anisotropic Self-Assembly of Poly(3-Hexylthiophene) (P3HT) during Channel Formation

Youngjun Kim,Byoung Nam Park

doi:10.3390/app10196886

Abstract

We probed ultrasound irradiation-induced structural ordering of poly(3-hexylthiophene) (P3HT) chains during solidification of a sonicated P3HT solution by monitoring the temporal evolution of the electrical and spectroscopic signals. We observed a peak source-drain current in the test devices during the electrical channel formation, followed by a significant decrease, which has not been observed in the pristine P3HT solution as the solvent evaporates. Through P3HT concentration-dependent gated-sheet conductance and in-situ Raman spectroscopy measurements during channel formation, we found that the competition between aggregation of the disentangled P3HT chains in solution by sonication and the concentration-dependent chain interactions with solvent evaporation led to a distinct electrical signature in the channel formation of the sonicated P3HT film compared to that of the pristine P3HT. The finding provides insights into new opportunities through optimization between the thermodynamic and kinetic considerations in designing pre-deposition treatments for enhanced charge transport.

Highlights

Microscopic studies of the P3HT film morphology have revealed that molecular ordering can be tuned through competition between nucleation and growth mechanisms depending on the degree of supersaturation [21]
The structural crystallinity of a solidified film after ultrasound irradiation of the P3HT solution was remarkably enhanced from the grazing incidence X-ray diffraction (GIXD) and photoluminescence (PL) measurements
The GIXD data of the spin-coated P3HT films with a distinct (100) diffraction peak in Figure 1a indicate, that π-π stack aggregation-induced molecular ordering is more prominent than that in the pristine P3HT, which is consistent with a lower PL intensity in the sonicated

Summary

Introduction

Enhancement of carrier mobility through molecular ordering has been an important issue in operating and optimizing flexible electronic devices that incorporate organic semiconductors [1,2,3,4,5,6,7,8]. Among various pre-deposition treatments including additive engineering, simple solution processing such as sonication-induced molecular ordering has attracted much attention due to dramatic mobility enhancement as well as its facile fabrication method [16,17,18,19,20] It is very well-known that ultrasound irradiation induces increased P3HT chain interactions in solution state through molecular aggregation, where more enhanced π-π stacking is achieved, enabling tuning of molecular crystallinity [9,16]. Unlike structure-property correlation based on the ex-situ analytical methods, we focus more on the kinetic-oriented approach in which the final film morphology and crystallinity are tuned through ultrasonic irradiation, resulting in the evolution of the structural arrangement of molecules in the solvent during the solidification process. Field-effect-modulated electrical properties were analyzed in correlation with the results from in-situ Raman spectroscopic measurements

Materials and Methods

Calculation of FET Mobility and Four-Point Sheet Conductance Measurement

Results and Discussion

For sonicated filmsP3HT