Effect of interchain interactions on the absorption and emission of poly(3-hexylthiophene)

Abstract

The absorption spectrum of polythiophene and its derivative poly͑3-hexylthiophene͒ ͑P3HT͒ is usually described in terms of an intrachain exciton coupled to a single phonon mode. We show that this model is too simplistic for highly ordered, regioregular P3HT and that, analogous to the case of charged polarons in this material, interchain interactions must be taken into account to correctly describe the absorption spectrum. We show that the lowest energy feature in the-* region of the absorption spectrum is associated with an interchain absorption, the intensity of which is correlated with the degree of order in the polymer. Correspondingly, we show that the emission from P3HT also exhibits contributions from both interchain and intrachain states, in a manner similar to that recently shown for poly͑phenylenevinylene͒. Having reinterpreted the physical origin of the features in the absorption and emission spectra of P3HT, we then model these spectra and show how they evolve as the degree of order in the polymer is changed by varying several physical parameters including temperature and regioregularity of the polymer.

π-Conjugated polymer-layered structures: synthesis and self-assembly

“…The main absorption peak of P3HT-P exhibited a further red-shift compared with that of P3HT-BDAN, with an absorption shoulder~600 nm corresponding to the crystalline P3HT domains in a single polymer chain. 47 In addition, hardly any emission was detected from P3HT-P. These results suggest that the P3HT units in P3HT-P adopted a well-stacked and more ordered arrangement in the solid state owing to the presence of the xanthene-based polymer scaffold.…”

Electronic Structure and Transition Energies in Polymer–Fullerene Bulk Heterojunctions

“…Brown et al performed a detailed sideband analysis and suggested that there are two exciton series in P3HT with overlapping sidebands. 8 However, they also concluded that the lowest energy exciton is the zerophonon transition. Spano showed that the HR intensities are modified by the molecular interactions in aggregated polymers.…”

“…8 The reorganization energy is described by a configurational coordinate diagram as shown in Figure 2b, which also illustrates the vibronic levels corresponding to the sidebands in the exciton absorption. 9,10 The general procedure to identify both the zero-phonon exciton energy and the reorganization energy is well established and is based on the relative intensities of the exciton absorption I(N) (N = 0, 1, 2, etc.)…”

“…The exciton couples primarily to the 0.17−0.18 eV group of phonons in conjugated organic semiconductors, as several papers have reported. 8,12 These are phonon modes of the conjugated rings that comprise the polymer backbone (e.g., CC stretching modes), 13 and they dominate the phonon coupling because the conjugated rings are the origin of the π-orbitals forming the exciton and hole wave functions. Coupling to the higher energy C−H modes is not observed because these bonds do not contribute to the π-orbitals.…”

Probing Electronic Structures of Organic Semiconductors at Buried Interfaces by Electronic Sum Frequency Generation Spectroscopy

“…There are at least four peaks in the UV-Vis spectra. The first three are from various inter/intramolecular interactions or vibronic modes 62,63 , where the long tail beyond 2.3 eV is attributed to oligomers that have short exciton delocalization 62 . Furthermore, all peaks are fitted into Gaussian lineshapes with fwhm between 0.14 to 0.30 eV (see SI), which indicates each peak is also inhomogeneous broadened.…”