Structure and X‐ray spectrum of crystalline poly(3‐hexylthiophene) from DFT‐van der Waals calculations

Abstract

The minimum-energy geometrical structure of the regioregular head-to-tail poly(3-hexylthiophene) (rr-HT-P3HT) polymer has been addressed by means of density functional theory (DFT) calculations which include long-range (van der Waals) interactions. The problem of the P3HT structure has been debated in the literature in the last decades mainly for what concerns the arrangement of the alkyl side chains of the polymer and the type and content of the crystalline primitive cell. The main result of our calculations is that the energetically favored structure of the crystalline polymer at T = 0 K corresponds to polythiophene chains with slightly (∼16°) non co-planar rings and a fishbone arrangement of tilted alkyl side chains with complex internal structure. The alkyl side chains are negligibly interdigitated with those of the adjacent polymer layers; moreover the five terminal carbon atoms of each alkyl side chain are co-planar in all-trans staggered conformation. The optimized geometrical structure obtained for the rr-HT-P3HT polymer is in agreement with measured X-ray spectra of high molecular weight P3HT crystalline samples, and confirms that two non-equivalent polymer chains, mutually shifted along the backbone axis, are contained in an orthorhombic primitive cell

Molecular design of new P3HT derivatives: Adjusting electronic energy levels for blends with PCBM

“…We also noticed, in all optimization calculations with different semiempirical methods, that the planes of the thiophene rings rotate up to 14 out of the initial common plane. Similar results are found in the literature for the P3HT, with more sophisticated calculations, using DFT with Periodic Boundary Contour (PBC) [33,38]. In their studies of polythiophenes and derivatives [44], S. S. Zade and M. Bendikov observed that, in the solid state, the same rotation can reach up to 36 .…”

A Study on the Correlation Between Structure and Hole Transport in Semi‐Crystalline Regioregular P3HT

“…A simple comparison between the length of a fully extended all-trans hexyl chain and the (100) d-spacing (See Supporting Information) also rules out the possibility of interdigitation, in agreement with previous experimental and theoretical results. [ 31,32 ] Based on the for charge carrier mobility ( μ ) is given by Equation 1 , where μ 0 is the mobility prefactor, σ /kT is the energetic disorder parameter (width of the density of states) normalized to thermal energy, Σ is the positional disorder parameter, E is the applied electric fi eld, k is the Boltzmann constant and C is an empirical constant.…”

Linear optical properties and electronic structures of poly(3-hexylthiophene) and poly(3-hexylselenophene) crystals from first principles

“…[20,29] To determine the stable crystal structure, several groups examined first-principles density functional theory (DFT) calculations, and discussed their structural properties. [30][31][32][33][34][35] However, most of these studies have been carried out using tentative orthorhombic lattices. The possibility that the material shows space groups with lower symmetry and its optical properties have not yet been theoretically discussed.…”