title: Compatibilization of All-Conjugated Polymer Blends for Organic Photovoltaics.
abstract: Compatibilization of an immiscible binary blend comprising a conjugated electron donor and a conjugated electron acceptor polymer with suitable electronic properties upon addition of a block copolymer (BCP) composed of the same building blocks is demonstrated. Efficient compatibilization during melt-annealing is feasible when the two polymers are immiscible in the melt, i.e. above the melting point of ∼250 °C of the semicrystalline donor polymer P3HT. To generate immiscibility at these high temperatures, the acceptor polymer PCDTBT is equipped with fluorinated side chains leading to an increased Flory-Huggins interaction parameter. Compatibilization in bulk and thin films is demonstrated, showing that the photovoltaic performance of pristine microphase separated and nanostructured BCPs can also be obtained for compatibilized blend films containing low contents of 10-20 wt % BCP. Thermodynamically stable domain sizes range between several tens of microns for pure blends and ∼10 nm for pure block copolymers. In addition to controlling domain size, the amount of block copolymer added dictates the ratio of edge-on and face-on P3HT crystals, with compatibilized films showing an increasing amount of face-on P3HT crystals with increasing amount of compatibilizer. This study demonstrates the prerequisites and benefits of compatibilizing all-conjugated semicrystalline polymer blends for organic photovoltaics.
authors.affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge , 19 J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom.|Makromolekulare Chemie, Universität Freiburg , Stefan-Meier-Straße 31, 79104 Freiburg, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Lombeck
authors.affiliation: Adolphe Merkle Institute , Chemin des Verdiers 4, CH-1700 Fribourg, Switzerland.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Sepe
authors.affiliation: Freiburger Materialforschungszentrum, Stefan-Meier-Straße 21, 79104 Freiburg, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Thomann
authors.affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge , 19 J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: Richard H
authors.initials: RH
authors.lastname: Friend
authors.affiliation: Makromolekulare Chemie, Universität Freiburg , Stefan-Meier-Straße 31, 79104 Freiburg, Germany.|Freiburger Materialforschungszentrum, Stefan-Meier-Straße 21, 79104 Freiburg, Germany.|FIT, Freiburger Zentrum für interaktive Werkstoffe und bioinspirierte Technologien, Georges-Köhler-Allee 105, 79110 Freiburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Sommer
mesh_terms: D049329:Nanostructures; D011108:Polymers
chemical_list: D011108:Polymers
keywords: P3HT; PCDTBT; compatibilization; donor−acceptor conjugated block copolymers; organic photovoltaics; phase separation; semifluorinated alkyl side chains; ternary conjugated polymer blends