Self‐Assembly of Rod‐Coil Block Copolymers for Photovoltaic Applications

Abstract

Summary: Two different approaches to obtain electron donor-acceptor interfaces via self-assembly of block copolymer systems are discussed, where the donor domains are formed by a p-conjugated rod-like polymer and the acceptor domains result from a coiled polymer modified by C 60 fullerenes. In the first strategy, C 60 is chemically grafted onto the coil polymer, typically a statistical copolymer of styrene and chloromethyl styrene. This has as major effect the increase in molecular weight and volume fraction of the coil block, which can markedly perturb the self-assembled block copolymer final morphologies and eventually suppress any microseparated nanostructure in favour of fully isotropic homogeneous phases. We discuss how the presence of free homopolymer rods in the system can help recovering a microphase separated morphology suitable for photovoltaic applications. In the second approach we discuss the poly(diethylhexyl-p-phenylenevinylene-b-4-vinylpyridine) (PPV-P4VP) rod-coil block copolymer system and we argue how supramolecular interactions among P4VP and free C 60 can be exploited to blend rod-coil block copolymers and C 60 preserving the original lamellar phase.

P4VP and oligo(phenylenevinylene)-perylenebisimide mixed donor-acceptor supramolecular comb polymer complexes with improved charge carrier mobility

“…One of the main objectives in the organic semiconducting material research is the ability to assemble donor (D) and acceptor (A) π‐conjugated materials in the nanoscopic length scale that promotes increased charge separation as well as long range pathway for charge transport to the respective electrodes. In the last decade, when the organic optoelectronic research was in the initial stages, a lot of interest was focused on the self‐assembly approach to assemble small molecules or oligomers of donor and acceptor molecules . Noted among them was the approach of incorporating complementary hydrogen bonding moieties like the imide and ureido pyrimidinone pair into donor‐acceptor (D‐A) pairs like perylenebisimide (PBI acceptor) and oligo( p ‐phenylenevinylene) (OPV donor) introduced by Meijer et al The melamine‐barbiturate/cyanurate and diaminopyrimidine‐thymine pairs also were studied in this pursuit for D‐A nano self‐assembly .…”

“…In the last decade, when the organic optoelectronic research was in the initial stages, a lot of interest was focused on the self-assembly approach to assemble small molecules or oligomers of donor and acceptor molecules. [19][20][21][22][23] Noted among them was the approach of incorporating complementary hydrogen bonding moieties like the imide and ureido pyrimidinone pair into donor-acceptor (D-A) pairs like perylenebisimide (PBI acceptor) and oligo(p-phenylenevinylene) (OPV donor) introduced by Meijer et al 22,23 The melamine-barbiturate/cyanurate and diaminopyrimidinethymine pairs also were studied in this pursuit for D-A nano self-assembly. 24,25 Although the association constant for these complementary hydrogen bonding D-A pairs were very high, they were plagued by formation of homo-stacks of the donor or acceptor leading to unwanted aggregation and macrophase separation and poor device performance.…”

A New Supramolecular Route for Using Rod‐Coil Block Copolymers in Photovoltaic Applications

“…Indeed, polyvinylpyridines are known to experience weak supramolecular interactions with electron-deficient chemical species. [38][39][40] These interactions would make free C 60 molecules preferentially accumulate within the coil domains and, when combined with an electron-donating rod block, lead to the endeavored D/A interpenetrated networks. Also, in the case of block copolymer/fullerene blends, the copolymer microphase separation has been found to be less affected by the C 60 crystallization than for fullerene-grafted block copolymers.…”

“…Also, in the case of block copolymer/fullerene blends, the copolymer microphase separation has been found to be less affected by the C 60 crystallization than for fullerene-grafted block copolymers. [34,39] In particular, the pristine DEH-PPV-b-P4VP nanostructure was shown to be preserved when blended with 10% C 60 and to be thermally stable up to at least 16 h at 180 8C. [39] Finally the PCBM fullerene derivative was chosen for its high solubility in common solvents.…”

“…[34,39] In particular, the pristine DEH-PPV-b-P4VP nanostructure was shown to be preserved when blended with 10% C 60 and to be thermally stable up to at least 16 h at 180 8C. [39] Finally the PCBM fullerene derivative was chosen for its high solubility in common solvents.…”