Conjugated polyelectrolyte (CPE) interfacial layers present a powerful way to boost the I-V characteristics of organic photovoltaics. Nevertheless, clear guidelines with respect to the structure of high-performance interlayers are still lacking. In this work, impedance spectroscopy is applied to probe the dielectric permittivity of a series of polythiophene-based CPEs. The presence of ionic pendant groups grants the formation of a capacitive double layer, boosting the charge extraction and device efficiency. A counteracting effect is the diminishing affinity with the underlying photoactive layer. To balance these two effects, we found copolymer structures containing nonionic side chains to be beneficial.
Funding Agencies|IAP project Functional Supramolecular Systems [7/05]; Science Policy Office of the Belgian Federal Government (BELSPO); Research Program of the Research Foundation Flanders (FWO) [G.0415.14N]; Foundation for Fundamental Research on Matter (FOM) from The Netherlands Organization for Scientific Research (NWO) [V0714M-13MV60]; Swedish Research Council Linnaeus LiLi-NFM at Linkoping University; Vrije Universiteit Brussel (VUB); University of Montpellier; CNRS; University of Mons