Highly Efficient n‐Doping via Proton Abstraction of an Acceptor<sub>1</sub>‐Acceptor<sub>2</sub> Alternating Copolymer toward Thermoelectric Applications
Adrian Hochgesang, Andreas Erhardt, John Mohanraj, Meike Kuhn, Eva M. Herzig, Selina Olthof, Mukundan Thelakkat
Abstract
Abstract Electron transporting ( n ‐type) polymers are the coveted complementary counterpart to more thoroughly studied hole transporting ( p ‐type) semiconducting polymers. Besides intrinsic stability issues of the doped form of n ‐type polymer toward ubiquitous oxidizing agents (H 2 O and O 2 ), the choice of suitable n ‐dopants and underlying mechanism of doping is an open research field. Using a low LUMO, n ‐type unipolar acceptor 1 ‐acceptor 2 copolymer poly(DPP‐TPD) in conjunction with bulk n ‐doping using Cs 2 CO 3 these issues can be addressed. A solid‐state acid‐base interaction between polymer and basic carbonate increases the backbone electron density by deprotonation of the thiophene comonomer while forming bicarbonate, as revealed by NMR and optical spectroscopy. Comparable to N‐DMBI hydride/electron transfer, Cs 2 CO 3 proton abstraction doping shifts the poly(DPP‐TPD) work function toward the LUMO. Thereby, the anionic doped state is resilient against O 2 but is susceptible toward H 2 O. Based on GIWAXS, Cs 2 CO 3 is mostly incorporated into the amorphous regions of poly(DPP‐TPD) with the help of hydrophilic side chains and has minor impact on the short‐range order of the polymer. Cs 2 CO 3 proton abstraction doping and the acceptor 1 ‐acceptor 2 copolymer architecture creates a synergistic n ‐doped system with promising properties for thermoelectric energy conversion, as evidenced by a remarkable power factor of (5.59 ± 0.39) × µW m −1 K −2 .