Polymorphisms and morphological studies of a difluorobenzothiadiazole conjugated copolymer with 7.8% polymer solar cell efficiency

Abstract

Structural analysis of PTh4FBT suggested that the highly crystalline nature of PTh4FBT is related to its zero c-shift co-facial packing.

The effect of alkyl side chain length on the formation of two semi-crystalline phases in low band gap conjugated polymers

“…20 While polymorphism is well known for small molecules and occurs in one in three compounds in the Cambridge Structural Database, 21,22 it has only been identified for a handful of p-conjugated polymers. [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] Presently there is no clear insight into the structural factors that cause polymorphism in small molecules or different semi-crystalline phases for a polymer. 22 In a recent study it has been shown that in small p-conjugated molecules short intermolecular contacts stabilize the threedimensional packing arrangement and prevent structural rearrangement to the enthalpically favored stabilized polymorph.…”

Regioregular and Random Difluorobenzothiadiazole Electron Donor–Acceptor Polymer Semiconductors for Thin-Film Transistors and Polymer Solar Cells

“…The UV–vis absorption spectra of the D–A polymers are presented in Figure , and their photophysical properties are summarized in Table . In hot dilute solutions (chlorobenzene, 90 °C), all polymers displayed the usual dual-band, broad featureless absorptions typical of D–A polymers (Figure a–e): a weak short-wavelength band attributable to localized π–π* transition (∼400 nm) and a strong broad long-wavelength band (540–570 nm) resulting from intramolecular charge transfer (ICT). ,,, When the solutions were cooled to room temperature, significant red-shifts of 40–120 nm in absorption maxima were noted, reflecting polymer aggregation to higher molecular orders with varying degrees of backbone coplanarity and accompanying higher degrees of π-delocalization along polymer backbone. The red-shifts were larger for high-MW random polymer, ran-P2 (Figure b), and mid- to high-MW regioregular polymers, reg-P2 and reg-P3 (Figure d,e), than for low-MW random material, ran-P1 (Figure a), with the red-shift of reg-P3 being most pronounced (∼120 nm).…”

Packing Principles for Donor–Acceptor Oligomers from Analysis of Single Crystals

“…For comparison with face-to-face πstacking, the aromatic rings of conjugated backbones in edgeto-face stacking have larger φ Ar−Ar . In the more extreme cases, the lateral chains even intercalate into the stacking of the conjugated backbones and completely degrade the close πstacking of the backbones, as is visible in the crystal structures of 2,7-di(2-thienyl)-9,9-dihexylfluorene (Figure 16a), 144 3′,3⁗,4,4⁗-tetrabutylhexathiophene, 142 As shown in Figure 18, 4,7-di(thiophen-2-yl)benzo-2,1,3thiadiazole (Th−BT−Th) 146 and 5,6-difluoro-4,7-di(thiophen-2-yl)benzo-2,1,3-thiadiazole (Th−FBT−Th) 52 stack into a roof top arrangement that differs from the herringbone arrangement of p-Ph 3 and Th 3 in Figure 6. In the herringbone packing, the edge of one oligomer interacts with the face of the other, whereas in the rooftop packing, the end of one oligomer points to the face of the terminal thienyl group of the other.…”

“…The main reasons are that the polydispersity and the long-chain structure of D–A polymers obscure the morphological influences of their building blocks. As the activation energies for the interaryl bond rotation are small, , the many rotatable single bonds on the backbone also result in a complicated conformational isomerism of the polymers. − Thus, the periodic lamellar packing and π-stacking, as indicated by the ( h 00) and the board (0 k 0) diffractions, are generally obtained from X-ray diffraction (XRD), ,,− but the periodic packing along the main-chain axis are seldom reported. So far, only few conjugated polymers have had their lattice structures solved; − the phase-separation morphologies of few representative polymer/fullerene bulk heterojunction layers have been investigated in detail. − Because the phase formation of the conjugated molecules is driven by weak physical interactions, polymorphism , and diverse packing disorders can also be introduced into bulk and thin-film samples of the conjugated polymers.…”