Conjugated polyelectrolytes (CPEs) are conjugated polymers bearing side-chain ionic functionalities likes anionic, cationic or zwitterionic groups1.
CPEs have emerged as new class of interfacial materials in thin film based electronic devices such as solar cells and OLEDs thanks to their ability to reduce the barrier between electrode and active layer resulting from the formation of an aligned interfacial dipole at the metal/organic semiconductor interface
CPEs have several advantages compared to conventional organic and inorganic interlayers like good solubility in polar solvent, included water, which allow deposition from orthogonal solvents and the possibility of tuning the optoelectronic and photophysical properties by tailoring the chemical structure of conjugated backbone and side-chains.
Recently, Bazan and coworkers2 have demonstrated anionic low bandgap CPEs polymer can be easily doped after dialysis in water and such doped conjugated polyelectrolytes, thanks to their pH-neutral nature are a promising alternative to acidic poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)3.
Although this kind of CPEs with pH neutral nature can be applied in perovskite based devices notoriously sensitive to the environment or as anode interfacial layer of OLEDs and OPVs with inverted geometry, currently there are only few materials with this characteristics and the material developed by Bazan remains the one with the best results.
In this logic, in order to obtain ever more effective CPE, it is particularly important to understand the role of the conjugated backbone and of the polar groups4,5.
Here we present the synthesis and preliminary optoelectrical characterization of two new donor-acceptor (D-A) anionic CPEs, one containing cyclopentadithiophene (CPDT) functionalized with one sulfonate terminated side-chain alternate to benzothiadiazole (BTD) units and the other containing a stronger donor unis, dithienopyrrole (DTP), functionalized with one carboxylate terminated side chain, alternate to BTD units.
The preliminary data confirmed the self doped nature of our CPEs but also a strong tendency to aggregation responsible for the poor quality of the films. Moreover sulfonate group seems to play a crucial role in the interfacial engineering.
