Phase Separation in the Melt and Confined Crystallization as the Key to Well-Ordered Microphase Separated Donor–Acceptor Block Copolymers

Abstract

Microphase-separated donor–acceptor block copolymers have been discussed as ideal systems for morphology control in organic photovoltaics. Typical microphases as known from coil–coil systems were not observed in such systems due to crystallization dominating over microphase separation. We show how this problem can be overcome by the synthesis of high molecular weight block copolymers leading to a high enough χN parameter and microphase separation in the melt. A combination of copper-catalyzed azide-alkyne click reaction and nitroxide mediated radical polymerization (NMRP) was used for the synthesis of donor–acceptor poly(3-hexylthiophene)-block-poly perylene bisimide acrylate (P3HT-b-PPerAcr) block copolymers. With this synthetic strategy, high molecular weights are possible and no triblock copolymer byproducts are formed, as observed with former methods. Two different block copolymers with a high molecular weight P3HT block of 19.7 kg/mol and a PPerAcr content of 47 and 64 wt % were obtained. X-ray scattering measurements show that the diblock copolymers exhibit microphase separation in the melt state. Furthermore, upon cooling confined crystallization occurs inside the microphase separated domains without destroying the microphase order. The observed microstructures fit well to the respective volume fractions and the crystalline packing within the individual blocks is analogous to those in the respective homopolymers. For the first time, typical lamellar or cylindrical phase separated structures as known for amorphous coil–coil systems are realized for a crystalline–liquid crystalline, donor–acceptor block copolymer. A similar block copolymer synthesized with an earlier method exhibits a crystallization-induced microphase separation.

Perylene Bisimide Dye Assemblies as Archetype Functional Supramolecular Materials

“…304 Recently, Thelakkat, Thurn-Albrecht, and co-workers have revealed the synthesis of donor−acceptor poly(3-hexylthiophene)-block-poly PBI acrylate (P3HT-b-PPerAcr) (3-51) and observed the microphase separation in melt and in subsequent confined crystallization without morphology change. 305 These crystalline liquid-crystalline, donor−acceptor diblock copolymers exhibited lamella and cylindrical phase separated structures depending on molecular weight and volume ratio between the two blocks analogous to amorphous coil−coil systems ( Figure 32). The charge transport properties of different morphologies in thin film were also investigated for these copolymers.…”

Effective Use of Electrically Insulating Units in Organic Semiconductor Thin Films for High‐Performance Organic Transistors

“…Compared with the p-type block copolymers, relatively few results are available for n-type block copolymers, possibly due to the difficulty of the synthetic method based on n-type conjugated backbones. [143][144][145][146][147][148][149][150][151][152][153][154][155][156][157][158][159][160][161] However, a study on donor-acceptor rod-coil diblock copolymers of P3HT and poly(2-phenyl-5-(4-vinylphenyl)-1,3,4-oxadiazole) (POXD) showed that the incorporation of the POXD acceptor would reduce the degree of order of P3HT leading to lower field-effect mobilities. [137,[142][143][144] Huettner et al synthesized a diblock copolymer consisting of poly(perylene bisimide acrylate) and PS.…”

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

“…Previous work on molecular donor-acceptor materials produced only modest power conversion efficiencies, a result attributed to a loss of charge carriers to recombination within the overly small domains. 16 Although there has been extensive work on block copolymers (BCPs) that employ pendant chromophores on a nonconjugated backbone, [17][18][19][20][21] to maximize chromophore density, the polymers should be fully conjugated. For these reasons, fully conjugated BCPs are the subject of this investigation.…”