New anionic Conjugated Polyelectrolytes for Interfacial engineering in Polymer Solar Cells

In the last years interfacial engineering has played a critical role in promoting the performance of organic solar cells (OSCs) since interfacial layers help to form an ohmic contact between the electrodes and the active layers, which is of great importance for charge collection. Conjugated polyelectrolytes (CPEs),which are conjugated polymers bearing side-chain ionic functionalities likes anionic, cationic or zwitterionic groups1, have emerged as new class of interfacial materials in thin film based electronic devices thanks to their ability to reduce the barrier between electrode and active layer. 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. There are mainly two kinds of interfacial materials which are commonly used in OSCs: electron-transporting layer (ETL) materials for electron extraction and hole-transporting layer (HTL) materials for hole extraction. The most common used HTL material in OSCs is acidic poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), thanks to his high optical transparency in the visible-NIR regime, suitable energy level, and sufficient conductivity. However his hygroscopic and acidic nature induces chemical instability between the electrodes and the active layer. Recently, Bazan and coworkers 2,3 and Chen and his groups4 have demonstrated CPEs, thanks to their pH-neutral nature are a promising alternative to PEDOT:PSS3. In this view, we have designed and synthesized a series of anionic copolymers with different ionic pendant groups using different conjugated backbones to obtain HTL materials. The functional behaviour of these copolymers as anode modifiers is herein investigated in polymer solar cell devices. (1) Hoven, C. V.; Garcia, A.; Bazan, G. C.; Nguyen, T.-Q. Adv. Mater. 2008, 20, 3793-3810. (2) Mai, C.-K.; Zhou, H.; Zhang, Y.; Henson, Z. B.; Nguyen, T.-Q.; Heeger, A. J.; Bazan, G. C. Angew. Chem. Int. Ed. 2013, 52, 12874-12878. (3) Zhou, H.; Zhang, Y.; Mai, C.-K.; Collins, S. D.; Nguyen, T.-Q.; Bazan, G. C.; Heeger, A. J. Adv. Mater. 2013, 26, 780-785. (4)Xu H., Fu X., Cheng X., Huang L., Zhou D., Chen L. J. Mater. Chem. A, 2017, 5, 14689-14696 .