Ionic Push–Pull Polythiophenes: A Further Step towards Eco-Friendly BHJ Organic Solar Cells

Abstract

Four new conjugated polymers alternating benzothiadiazole units and thiophene moieties functionalized with ionic phosphonium or sulfonic acid salts in the side chains were synthesized by a postfunctionalization approach of polymeric precursors. The introduction of ionic groups makes the conjugated polymers soluble in water and/or polar solvents, allowing for the fabrication of bulk heterojunction (BHJ) solar cells using environmentally friendly conditions. All polymers were fully characterized by spectroscopic, thermal, electrochemical, X-ray diffraction, scanning electron, and atomic force techniques. BHJ solar cells were obtained from halogen-free solvents (i.e., ethanol and/or anisole) by blending the synthesized ionic push–pull polymers with a serinol-fullerene derivative or an ionic homopolymer acting as electron-acceptor (EA) or electron-donor (ED) counterparts, respectively. The device with the highest optical density and the smoothest surface of the active layer was the best-performing, showing a 4.76% photoconversion efficiency.

Effects of Water/Alcohol Soluble Cationic Polythiophenes as Cathode Interlayers for Eco‐Friendly Solar Cells

“…Polymer films were deposited on Pt disk electrode (diameter 1 mm) by drop casting from methanol solutions. Auxiliary electrode was Pt spiral and potential reference was aqueous Saturated Calomel Electrode (SCE) whose absolute potential was assumed −4.24 V. [ 31 ]…”

“…Polymer films were deposited on Pt disk electrode (diameter 1 mm) by drop casting from methanol solutions. Auxiliary electrode was Pt spiral and potential reference was aqueous Saturated Calomel Electrode (SCE) whose absolute potential was assumed −4.24 V. [31] X-ray diffraction (XRD) data were recorded at room temperature by using a Cu K𝛼 (𝜆 = 1.5406 Å) radiation source (Philips PW 1050) and a Bragg-Brentano diffractometer (Philips PW 1710) equipped with a graphite monochromator in the diffracted beam. The 2𝜃 range between 2.0°and 90.0°was scanned by 881 steps of 0.1°with a counting time of 15 s for each step.…”