Highly Efficient n-Doping via Proton Abstraction of an Acceptor(1)-Acceptor(2) Alternating Copolymer toward Thermoelectric Applications

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 (H2O 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 Cs2CO3 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, Cs2CO3 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 H2O. Based on GIWAXS, Cs2CO3 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. Cs2CO3 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) x mu W m(-1) K-2.