Enhanced n-Doping Efficiency of a Naphthalenediimide-Based Copolymer through Polar Side Chains for Organic Thermoelectrics

David Kiefer; Alexander Giovannitti; Hengda Sun; Till Biskup; Anna Hofmann; Marten Koopmans; Camila Cendra; Stefan Weber; L Jan Anton Koster; Eva Olsson; Jonathan Rivnay; Simone Fabiano; Iain McCulloch; Christian Müller

doi:10.1021/acsenergylett.7b01146

Enhanced n-Doping Efficiency of a Naphthalenediimide-Based Copolymer through Polar Side Chains for Organic Thermoelectrics

ACS Energy Lett. 2018 Feb 9;3(2):278-285. doi: 10.1021/acsenergylett.7b01146. Epub 2018 Jan 5.

Authors

Affiliations

¹ Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 412 96 Göteborg, Sweden.
² Department of Chemistry and Centre for Plastic Electronics, Imperial College London, London SW7 2AZ, United Kingdom.
³ Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, 601 74 Norrköping, Sweden.
⁴ Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany.
⁵ Zernike Institute for Advanced Materials, 9747 AG Groningen, The Netherlands.
⁶ Department of Materials Science and Engineering, Stanford University, Stanford, California 94304, United States.
⁷ Department of Physics, Chalmers University of Technology, 412 96 Göteborg, Sweden.
⁸ Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60035, United States.
⁹ SPERC, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia.

Abstract

N-doping of conjugated polymers either requires a high dopant fraction or yields a low electrical conductivity because of their poor compatibility with molecular dopants. We explore n-doping of the polar naphthalenediimide-bithiophene copolymer p(gNDI-gT2) that carries oligoethylene glycol-based side chains and show that the polymer displays superior miscibility with the benzimidazole-dimethylbenzenamine-based n-dopant N-DMBI. The good compatibility of p(gNDI-gT2) and N-DMBI results in a relatively high doping efficiency of 13% for n-dopants, which leads to a high electrical conductivity of more than 10^-1 S cm^-1 for a dopant concentration of only 10 mol % when measured in an inert atmosphere. We find that the doped polymer is able to maintain its electrical conductivity for about 20 min when exposed to air and recovers rapidly when returned to a nitrogen atmosphere. Overall, solution coprocessing of p(gNDI-gT2) and N-DMBI results in a larger thermoelectric power factor of up to 0.4 μW K^-2 m^-1 compared to other NDI-based polymers.