Polar conjugated polymers: eco-friendly materials as new frontier of organic semiconductors

The development of new materials plays a key role for the exploitation of the new technologies. One important class of emerging semiconducting materials is represented by conjugated polyelectrolytes (CPEs) comprising an electronically delocalized ?-conjugated backbone with pendant groups bearing polar or ionic functionalities. CPEs bring together the typical properties of polymeric semiconductors, such as easy processability, chemical tunability, lightness and flexibility with the growing demand for environmentally friendly materials. In fact, the incorporation of polar/ionic side groups increases the solubility in water and alcohols, which can potentially provide increased biocompatibility for sensor applications and more environmentally friendly manufacturing options. Moreover, the possibility for orthogonal solvent processability opens the way to all-solution-processed organic multilayer devices. Interfacial engineering has been identified recently as an essential approach for maximizing efficiency and stability of electronic devices. In this contest, the intrinsic hybrid characteristics of CPEs make them promising candidates for tuning the interface properties of inorganic materials too. We have recently shown that the insertion of a thin CPE film between active layer and cathode in organic electronic devices results in the energy level tuning at the CPE/metal interface, which is crucial for achieving a high-performance device, due to the formation of permanent dipoles . In this view, we have designed, synthesized and tested CPEs featuring a fluorene-based backbone with pendant phosphonate and/or amine groups and we have tested them in different types of devices. In particular by comparing the effect of CPEs on OLEDs and OPVs behavior, we focus on the influence of the electrical conditioning of the CPE layer on the device performance. The same class of CPEs, thanks to their conjugated backbone and ionic functionality have shown to remarkably enhance the pseudocapacitance of MXene-based hybrid 2D materials .