Raman spectroscopy as an advanced structural nanoprobe for conjugated molecular semiconductors

Abstract

Raman spectroscopy has emerged as a powerful and important characterisation tool for probing molecular semiconducting materials. The useful optoelectronic properties of these materials arise from the delocalised -electron density in the conjugated core of the molecule, which also results in large Raman scattering cross-sections and a strong coupling between its electronic states and vibrational modes. For this reason, Raman spectroscopy offers a unique insight into the properties of molecular semiconductors, including: chemical structure, molecular conformation, molecular orientation, and fundamental photo-and electro-chemical processes-all of which are critically important to the performance of a wide range of optical and electronic organic semiconductor devices. Experimentally, Raman spectroscopy is non-intrusive, non-destructive, and requires no special sample preparation, and so is suitable for a wide range of in situ measurements, which are particularly relevant to issues of thermal and photochemical stability. Here we review the development of the family of Raman spectroscopic techniques, which have been applied to the study of conjugated molecular semiconductors. We consider the suitability of each technique for particular circumstances, and the unique insights it can offer, with a particular focus on the significance of these measurements for the continuing development of stable, high performance organic electronic devices.

Efficient Charge Carrier Injection and Balance Achieved by Low Electrochemical Doping in Solution‐Processed Polymer Light‐Emitting Diodes

“…The thickness of active layer, ≈150 nm was used to increase the range of voltages that can be applied. The Raman peaks of neat F8BT, 1314, 1357, 1425, 1457, 1486, 1545, and 1608 cm −1 , are well known and supported by our density functional theory (DFT) calculation at B3LYP 6.31G(d,p) (the details of the DFT calculations are provided in Figure S13, Supporting Information) . When voltages between 0 and 7 V were applied to the neat F8BT PLEDs, there were no changes in the Raman spectra ( Figure a).…”

Molecular understanding of a π-conjugated polymer/solid-state ionic liquid complex as a highly sensitive and selective gas sensor

“…Such field-dependent conductivity tuning is expected to originate from intermolecular interactions between P3HT and the SSIL, and thus Raman spectroscopy was conducted to gain insights into the chemical structure, molecular conformation, and p-electron density distribution in P3HT. 39 The normalised Raman spectroscopy ( Fig. S8 in the ESI †) shows that blending with the SSIL does not affect peak positions or relative intensities compared to the neat P3HT film.…”

From fullerene acceptors to non-fullerene acceptors: prospects and challenges in the stability of organic solar cells

“…Due to this sensitivity to polarisable electron density, Raman spectroscopy can probe molecular conformation as well as chemical structure. 120 This has been utilised for investigating the molecular conformation and morphology of several polymers within BHJ blends. [121][122][123][124] These spectroscopies have also allowed for the elucidation of several degradation mechanisms at a molecular level.…”