Highly Efficient Doping of Conjugated Polymers using Multielectron Acceptor Salts.

Chemical doping is a vital tool for tuning electronic properties of conjugated polymers. Most single electron acceptors necessitate high doping concentrations to achieve good electrical conductivities. However high molar doping ratios hamper doping efficiency. Here a new concept of using multielectron acceptor (MEA) salts as dopants for conjugated polymers is presented. Two novel MEA salts are synthesized and their doping efficiency towards two polymers differing in their dielectric properties are compared with two single electron acceptors such as NOPF6 and magic blue. Cutting-edge methods such as UPS/XPS, Impedance spectroscopy, XPS mapping and DOS analysis in addition to UV-VIS-NIR absorption, spectroelectrochemistry and Raman spectroscopy methods are used to characterize the doped systems. The tetracation salt improves the conductivity by two orders of magnitude and quadruples the charge carrier concentration compared to single electron acceptors for the same molar ratio. The differences in charge carrier density and activation energy on doping are delineated. Further, a strong dependency of the carrier release on the polymer polarity is observed. High carrier densities at reduced dopant loadings and improved doping efficacies using MEA dopants offer a highly efficient doping strategy for conjugated polymers. Less is more: Tetracationic organic dopants can induce a four-fold charge carrier density in organic semiconducting polymers compared to monovalent dopants for the same dopant ratio, which helps minimizing dopant loading and negative effects on charge transport (see picture). We show that polymer polarity is a decisive factor to achieve high doping efficiencies. This article is protected by copyright. All rights reserved.