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

Three new ionic polythiophene derivatives, soluble in polar solvents, are synthesized with good yields using simple, low-cost, and straightforward procedures. They are investigated as interfacial cationic conjugated polyelectrolyte (CPE) layers for halogen-free bulk heterojunction polymeric solar cells, based on a water-soluble electron-donor polymer (poly[3-(6-diethanolaminohexyl)thiophene]) and a water-soluble electron-acceptor fullerene derivative (malonodiserinolamide fullerene). The simple insertion of the CPE interlayer between the active layer and the aluminum cathode dramatically increases the power conversion efficiency of the final device up to nearly 5%, resulting from a decrease of the electrode work function, improved electron extraction, and optimization of the morphology of the layers. The obtained results demonstrate that the incorporation of CPE layer is a powerful and convenient methodology for the development of highly efficient and eco-friendly processable polymeric solar cells.