Sketch of the structure of PBTTT-C14 and several important structure parameters considered in this work.
Comparisons between the single isolated chain and the π-stacked structure of PBTTT-C14: (a) the total energy as a function of the backbone tilt angle θ2; (b) the total energy as a function of torsion angle θ1 between the side-chain and the backbone; (c) the dependence of bandgap on θ1; and (d) the dependence of π-stacking distance on θ1. All results are based on fully relaxed structures except (a).
Density of states (DOS) of (a) the single isolated chain, and (b) the π-stacked PBTTT-C14. The Fermi energy is set to zero.
Band structures of (a) the single isolated chain, and (b) the π-stacked PBTTT-C14. The high symmetry k-points are Γ(0.0, 0.0, 0.0), Y(0.0, 0.5, 0.0), Q(0.0, 0.5, 0.5), Z(0.0, 0.0, 0.5), and X(0.5, 0.0, 0.0); the Fermi energy is set to zero.
Wave functions of the valence band maximum (VBM) and conduction band minimum (CBM) at Z(0.0, 0.0, 0.5) and Q(0.0, 0.5, 0.5) for the π-stacked PBTTT-C14, plotted with isosurface value of 0.016 bohr−3/2 (yellow) and −0.016 bohr−3/2 (blue).
(a) The imaginary part of the dielectric function calculated with GGA for the π-stacked PBTTT-C14. P1-P5 are the selected peaks in the spectrum; a magnified view of the low-energy section is shown in the inset to include P3, P4, and P5 peaks; (b) associated transitions are shown in arrows in the band structure; (c) ɛ ″ calculated with B3LYP functional; (d) ɛ ″ for the isolated PBTTT-C14 chain calculated with GGA.
Structure parameters, bandgaps, and relative energies of the π-stacked PBTTT-C14. Expt: experimental values; MM: results from the molecular mechanics calculation.
Critical-point (CP) energies of the π-stacked PBTTT-C14. Z, Q, Γ, and Y denote high symmetry k-points of the Brillouin zone; v1 is the first valence band labeled downward from the Fermi level, and c1 labels the first conduction band counted upward from the Fermi level.
Article metrics loading...
Full text loading...