Polythiophene-block-polyfluorene and Polythiophene-block-poly(fluorene-co-benzothiadiazole): Insights into the Self-Assembly of All-Conjugated Block Copolymers

Abstract

All-conjugated block copolymers have significant potential for solution-processed optoelectronic applications, in particular those relying on a p/n junction. Herein, we report the synthesis and structure of all-conjugated diblock copolymers poly(3-hexylthiophene)-block-poly(9,9-dioctylfluorene) and poly (3-hexylthiophene)-block-poly(9,9-dioctylfluorene-co-benzothiadiazole) in thin films and in the bulk. The diblock copolymers are prepared using a combination of Grignard metathesis polymerization and Suzuki polycondensation and characterized with NMR spectroscopy, size-exclusion chromatography, multiangle laser light scattering, and UV/vis spectroscopy. Structure in thin films and in the bulk is characterized using differential scanning calorimetry, X-ray diffraction, small-angle X-ray scattering, and atomic force microscopy. Diblock copolymer thin films self-assemble into a crystalline nanostructure with some long-range order after extended solvent annealing, and X-ray scattering measurements show that powder samples exhibit crystallinity throughout the bulk. By temperature dependent X-ray scattering measurements, we find that diblock copolymers self-assemble into crystalline nanowires with phase segregated block copolymer domains. These measurements show all-conjugated diblock copolymers may be useful for achieving solution-processed active layers in organic photovoltaics and light-emitting diodes with optimized structural and photophysical characteristics.

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

“…This result contrasts that observed in CBCPs of P3HT with polyfluorenes where the weight fraction of the polymer was found to control which block dominates the initial ordering. 39,78 The melt temperature of DPPT-T is higher than that for P3HT, but the difference is not large indicating that aggregation (solvent quality) has a more critical role than molecular weight for this system.…”

“…This goal has been met by BCPs where either one block has a conjugated backbone and the other has an insulating backbone with pendant conjugated molecules, [29][30][31][32][33][34][35][36][37] or by structures where both blocks have conjugated backbones (CBCPs). [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] Because of the relative stiffness of conjugated backbones, the phase separation of their BCP is complex due to energetic interactions between blocks, the volume fraction of the blocks, and potential crystallization.…”

Block copolymer strategies for solar cell technology

“…[37][38][39]105,109 When rod-based block copolymers are extensively annealed, long range order is commonly observed in the form of nanowires or fibrils. [110][111][112][113] The individual wires consist of aligned rod blocks and have been shown to be particularly valuable for charge mobility. It should be stressed, however, that all of the aforementioned nanostructures are dependent on the processing history of the polymer.…”

Engineering of Energy Levels for Fully Conjugated D‐A Block Copolymers via Tuning the Ratios of Donor P3HT and Acceptor PNDIT

“…[15] A similar strategy has also been used extensively to prepare analogues of PF-b-P3HT by Verduzco and co-workers. [16] (ii) Polymerization reaction of AA＋BB type bifunctional monomer with end-functional P3HT. The synthesis of P3HT-b-PFTBT was realized by palladium catalyzed Suzuki-Miyaura polymerization of AA＋BB type bifunctional monomer in the presence of P3HT-Br as an end-capper, and use of block copolymer P3HT-b-PFTBT as the single active material in all-polymer solar cell devices exhibiting nearly 3% efficiency.…”