Interplay of Intramolecular Noncovalent Coulomb Interactions for Semicrystalline Photovoltaic Polymers

Abstract

Four different kinds of photovoltaic polymers were synthesized by controlling the intrachain noncovalent coulomb interactions through the incorporation of alkoxy-or alkylthio substituted phenylene, 4,7-di(furan-2-yl)benzothiadiazole and 4,7-di(thiophen-2-yl)benzothiadiazole as a building block. Fine-modulation of the interplay of dipole-dipole, H-bond and chalcogen-chalcogen interactions (O•••S, O•••H, S•••S, S•••F, etc.) along the polymeric backbone influenced the chain planarity, interchain organization, film morphology, electrical, and photovoltaic properties significantly. By replacing the alkoxy substituents with alkylthio groups, the torsional angle increased (136~168°) due to the absence of an O•••S attractive coulomb interaction (and/or increased S•••S steric hindrance), enhancing the amorphous nature with hindered interchain packing. The alkoxy-substituted polymers exhibited nanofibrillar structures, showing strong interlamellar scattering peaks up to (300) with tight face-on π-π stacking in grazing incidence X-ray scattering. The measured carrier mobility of the alkoxy-containing polymers was 1~2 orders of magnitude higher than that of the alkylthio-containing polymers. The incident-light-intensity-dependent photovoltaic characteristics clearly suggested efficient charge generation/extraction with less charge recombination for the alkoxy-containing semi-crystalline polymers. The resulting photovoltaic energy conversion efficiency of the PPDT2FBT, PPDF2FBT, PPsDF2FBT and PPsDT2FBT blended devices with PC70BM was measured to be 8.28, 5.63, 5.12, and 0.55%, respectively. This study suggests an important molecular design guideline for the further optimization of photovoltaic polymers and devices by fine-controlling the interplay of the weak noncovalent coulomb interactions.

Donor polymer design enables efficient non-fullerene organic solar cells

“…It is clear that the positions of the fluorine atoms dictate the relative orientation of the thiophene units. Similar observations of F–S interactions determining the conformation or geometry of neighbouring aromatic units have been reported before39. These two isomers are referred to as T–FB–T-P or T–FB–T-O respectively and the two polymers are named as PTFB-P and PTFB-O.…”

Small Changes With Big Consequences: Swapping Two Atoms In Side Chains Changes Phenylene‐Ethynylene Packing And Fluorescence

“…Guiding assemblyo fc onjugated small molecules and polymers through directional non-covalent interactions of main chains such as hydrogen bonding, [3][4][5] halogen bonding, [6,7] and chalcogen interactions is increasingly common. [8,9] Given the ubiquity of aromatic rings in these materials, cofacial stacking interactions between electron-poorf luorinated arenes and electronrich arenes can be powerfuls upramoleculars ynthons in designing luminescent, electronic, and stimuli-responsive solids. [10][11][12][13][14] Even though they can occupy large proportions of conjugated materials, the primary purposeo fs ide chains is usuallyt o induces olubility.I nc ontrast, our group has harnessed this chemicals pace through "side-chain engineering" [15] to increase the functional role of non-conjugated pendantst hrough discrete non-covalenti nteractions of arenes.…”

Blade‐Cast Nonfullerene Organic Solar Cells in Air with Excellent Morphology, Efficiency, and Stability

“…Considering the different optimal DIO contents needed for the best spin‐coated and blade‐coated devices, the spin‐coated device with 1% DIO and blade‐coated device with 0.25% DIO are employed to study the charge dynamics involving charge generation and extraction characteristics as well as the recombination mechanism . Figure d presents the photocurrent density ( J ph ) versus the effective voltage ( V eff ) of various devices.…”