Control of Intrachain Charge Transfer in Model Systems for Block Copolymer Photovoltaic Materials

Abstract

We report the electronic properties of the conjugated coupling between a donor polymer and an acceptor segment serving as a model for the coupling in conjugated donor-acceptor block copolymers. These structures allow the study of possible intrachain photoinduced charge separation, in contrast to the interchain separation achieved in conventional donor-acceptor blends. Depending on the nature of the conjugated linkage, we observe varying degrees of modification of the excited states, including the formation of intrachain charge transfer excitons. The polymers comprise a block (typically 18 repeat units) of P3HT, poly(3-hexyl thiophene), coupled to a single unit of F8-TBT (where F8 is dioctylfluorene, and TBT is thiophene-benzothiadiazole-thiophene). When the P3HT chain is linked to the TBT unit, we observe formation of a localized charge transfer state, with red-shifted absorption and emission. Independent of the excitation energy, this state is formed very rapidly (<40 fs) and efficiently. Because there is only a single TBT unit present, there is little scope for long-range charge separation and it is relatively short-lived, <1 ns. In contrast, when the P3HT chain and TBT unit are separated by the wider bandgap F8 unit, there is little indication for modification of either ground or excited electronic states, and longer-lived charge separated states are observed.

The synthesis and purification of amphiphilic conjugated donor–acceptor block copolymers

“…In addition, an intriguing aspect of these BCPs is that the interface between donor and acceptor is defined covalently and so allows rational design for optimized charge transfer. 33,34 Homopolymer contaminants dilute this capability. Despite these considerations, difficulties with purification have meant that analysis of fully conjugated BCPs has typically involved polymeric mixtures.…”

Role of Solution Structure in Self-Assembly of Conjugated Block Copolymer Thin Films

“…improved donor-acceptor pairs, or if the covalent linkage of the donor and acceptor in the BCP leads to detrimental recombination or interfacial electronic states. 54,[59][60][61] Additionally, there are also significant questions concerning the role of purity of the donor and acceptor domains in BHJs on charge recombination. 62,63 A fundamental understanding of how the nanostructure and molecular order in CBCPs evolves will help to answer these questions.…”

Enhancing Ordering Dynamics in Solvent-Annealed Block Copolymer Films by Lithographic Hard Mask Supports

“…in high-resolution lithography, 2 in the behavior of liquid crystal displays, 3 in organic photovoltaic [4][5][6] and in sensoring devices. 7 Also, a slow chain dynamics during annealing protocols of microphase separated structures in block copolymers films 8 is a limiting factor in developing cost-effective nanoscale patterning technologies.…”