Precise Characterisation of Molecular Orientation in a Single Crystal Field-Effect Transistor Using Polarised Raman Spectroscopy

Abstract

Charge transport in organic semiconductors is strongly dependent on the molecular orientation and packing, such that manipulation of this molecular packing is a proven technique for enhancing the charge mobility in organic transistors. However, quantitative measurements of molecular orientation in micrometre-scale structures are experimentally challenging. Several research groups have suggested polarised Raman spectroscopy as a suitable technique for these measurements and have been able to partially characterise molecular orientations using one or two orientation parameters. Here we demonstrate a new approach that allows quantitative measurements of molecular orientations in terms of three parameters, offering the complete characterisation of a three-dimensional orientation. We apply this new method to organic semiconductor molecules in a single crystal field-effect transistor in order to correlate the measured orientation with charge carrier mobility measurements. This approach offers the opportunity for micrometre resolution (diffraction limited) spatial mapping of molecular orientation using bench-top apparatus, enabling a rational approach towards controlling this orientation to achieve optimum device performance.

A Three‐Dimensional Porous Organic Semiconductor Based on Fully sp2‐Hybridized Graphitic Polymer

“…A Raman spectrum of the 3D p‐POP (Figure d) obtained under excitation at 325 nm exhibits two strong peaks at 1387 and 1589 cm −1 . These can be attributed to C−C ring stretching vibration, A g mode, and in plane vibrational mode, B 3g , respectively, and match well the Raman bands of pentacene, further confirming that the 3D p‐POP has molecular connectivity based on pentacene moieties. Generally, linear polyacene molecules such as pentacene are known to be kinetically unstable under ambient atmospheric conditions in the presence of light and air, in which the molecule undergoes photooxidation.…”

“…A Raman spectrum of the 3D p-POP (Figure 2 d) obtained under excitation at 325 nm exhibits two strong peaks at 1387 and 1589 cm À1 . These can be attributed to CÀC ring stretching vibration, A g mode, and in plane vibrational mode, B 3g , respectively, and match well the Raman bands [17] of pentacene, further confirming that the 3D p-POP…”

A Three‐Dimensional Porous Organic Semiconductor Based on Fully sp2‐Hybridized Graphitic Polymer

“…A Raman spectrum of the 3D p-POP (Figure 2 d) obtained under excitation at 325 nm exhibits two strong peaks at 1387 and 1589 cm À1 . These can be attributed to CÀC ring stretching vibration, A g mode, and in plane vibrational mode, B 3g , respectively, and match well the Raman bands [17] of pentacene, further confirming that the 3D p-POP has molecular connectivity based on pentacene moieties. Generally, linear polyacene molecules such as pentacene are known to be kinetically unstable under ambient atmospheric conditions in the presence of light and air, in which the molecule undergoes photooxidation.…”

Two‐Step Synthesis of Large‐Area 2D Bi2S3 Nanosheets Featuring High In‐Plane Anisotropy

“…This may be required when electrode alignment with the crystal structure is critical, particularly in light of the high degree of anisotropy. [25]…”