Ternary Photovoltaic Blends Incorporating an All-Conjugated Donor–Acceptor Diblock Copolymer

Abstract

We present a new fully conjugated diblock copolymer, P3HT-b-PFTBTT, containing donor and acceptor blocks with suitably positioned energy levels for use in a solar cell. This is the first block copolymer to be based on an existing high-performance polymer:polymer blend. We observe phase separation of the blocks and self-assembly behavior. In ternary blends with the respective homopolymers the diblock copolymer introduces lateral nanostructure without restricting P3HT crystallization in the charge transport direction, resulting in standing lamellae. By adding the diblock to the homopolymer blend as a compatibilizer, we prevent phase separation at elevated temperatures and benefit from a dramatic increase in P3HT ordering, allowing us to demonstrate polymer blend photovoltaics where the nanostructure is thermodynamically, rather than kinetically, controlled.

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

“…In contrast, the addition of solubilizing hexyl side chains to the TBT unit in P3HT-b-PF TEG T6BT increases the monomer's solubility and markedly reduces the amount of triblock copolymer produced. Although the percentages of BCP present in the crude polymer mixtures are low (21 and 32%), they are not unreasonable when compared with previous reports for this type of BCP synthesis 23,35 and emphasize the value of a purification technique capable of isolating the BCP product.…”

Morphological Control Agent in Ternary Blend Bulk Heterojunction Solar Cells

“…Similar to the cases reviewed above, a compatibilizing copolymer composed of the molecular structures of both donor and acceptor can be used to bridge the binary phases and control the phase-separated morphology in nanoscale. Mulherin et al synthesized an all-conjugated diblock copolymer poly(3-hexylthiophene)-block-poly[2,7-(9,9-dialkyl-fluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (P3HT-b-PFTBTT) for mediating the P3HT/PFTBTT polymer-polymer blend BHJ [42]. The copolymer was discovered to suppress the phase separation along lateral direction while remain the crystallization of P3HT along the vertical direction [42].…”

“…Mulherin et al synthesized an all-conjugated diblock copolymer poly(3-hexylthiophene)-block-poly[2,7-(9,9-dialkyl-fluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (P3HT-b-PFTBTT) for mediating the P3HT/PFTBTT polymer-polymer blend BHJ [42]. The copolymer was discovered to suppress the phase separation along lateral direction while remain the crystallization of P3HT along the vertical direction [42]. Furthermore, the standing lamellar structure with size of 25 nm was induced by the copolymer inside the thin film (Figure 3d), which is comparable to exciton diffusion length and facilitates charge transport.…”

Polymer solar cells

“…For more detail, and in particular for full references to background and related work, the reader is referred to the original papers describing the work [24][25][26].…”