Ionic Dopant‐Induced Ordering Enhances the Thermoelectric Properties of a Polythiophene‐Based Block Copolymer

Abstract

Conjugated polymer-based block copolymers (CP-BCPs) are an unexplored class of materials for organic thermoelectrics. Herein, the authors report on the electronic conductivity (σ) and Seebeck coefficient (α) of a newly synthesized CP-BCP, poly(3-hexylthiophene)-block-poly (oligo-oxyethylene methacrylate) (P3HT-b-POEM), upon solution co-processing with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and subsequently vapor-doping with a molecular dopant, 2,3,5,6-tetrafluoro-7,7,8,8tetracyanoquinodimethane (F4TCNQ). It is found that the addition of the hydrophilic block POEM greatly enhances the processability of P3HT, enabling homogeneous solution-mixing with LiTFSI. Notably, interactions between P3HT-b-POEM with ionic species significantly improve molecular order and unexpectedly cause electrical oxidizing doping of P3HT block both in solution and solid-states, a phenomenon that has not been previously observed in Li-salt containing P3HT. Vapor doping of P3HTb-POEM-LiTFSI thin films with F4TCNQ further enhances σ and yields a thermoelectric power factor PF = α 2 σ of 13.0 µW m −1 K −2 , which is more than 20 times higher than salt-free P3HT-b-POEM sample. Through modeling thermoelectric behaviors of P3HT-b-POEM with the Kang-Snyder transport model, the improvement in PF is attributed to higher electronic charge mobility originating from the enhanced molecular ordering of P3HT.The results demonstrate that solution co-processing CP-BCPs with a salt is a powerful method to control structure and performance of organic thermoelectric materials.

Using Bulky Dodecaborane-Based Dopants to Produce Mobile Charge Carriers in Amorphous Semiconducting Polymers

“…Surprisingly, doping of RRa P3HT with DDB-F 72 produces a set of dopant-intercalated lamellar and π-stacking peaks (Figures d and ) that are identical to those of doped RR P3HT. This indicates that the amorphous RRa P3HT undergoes dopant-induced ordering, resulting in ordered crystallites, with a doped crystal structure that is the same as that of doped RR P3HT. ,, …”

“…This indicates that the amorphous RRa P3HT undergoes dopant-induced ordering, resulting in ordered crystallites, with a doped crystal structure that is the same as that of doped RR P3HT. 31,34,59 The presence of higher-order lamellar overtones and sharper lamellar peaks in the integrated patterns for doped RRa P3HT compared to RR P3HT (Figure 6) indicate that RRa P3HT has larger doped crystallites than RR P3HT. However, the overtones fade much faster in RRa P3HT than RR P3HT (Figure 6a,b), indicating that while RR P3HT crystallites may be smaller, they retain a higher level of paracrystalline order than the RRa P3HT polymer, 60,61 as determined by GISAXS.…”

High Vertical Hole Mobility through Minimization of Water-Induced Traps by F4TCNQ Doping in Conjugated Amphiphilic Diblock Copolymers

“…At c = 0.1 mg mL −1 , the absorption bands corresponding to neutral F4TCNQ (390 nm), anionic F4TCNQ (410, 760, and 860 nm), and polaron (760 and 860 nm) were clearly seen. 30,31 When c increased from 0.3 to 0.8 mg mL −1 , the absorption bands corresponding to the neutral F4TCNQ (390 nm) and the anionic F4TCNQ (410 nm) increased gradually. At c > 0.8 mg mL −1 , there were no further changes in the absorption bands of the anionic F4TCNQ, indicating that the HM film was fully doped with a molar concentration of 5.02 × 10 −4 mol cm −3 at c = 0.8 mg mL −1 (Figure 3b).…”

Tellurium/polymers for flexible thermoelectrics: status and challenges

“…Solubility makes P3HT an applicable polymer matrix for various solution-processes in thermoelectric hybrid systems. [198][199][200][201][202] For example, Graham et al 133 synthesized Te/P3HT hybrid lms through drop casting the mixture solution containing Te NWs and P3HT solution. The energetics at the Te/P3HT interfaces were adjusted by doping P3HT with different contents of FeCl 3 .…”