Photovoltaic devices from self-doped polymers

Abstract

Over the last decade, conjugated polymer-based semiconductors have been developed as a novel class of photovoltaic materials that have the potential to lower costs. Solvent based polymers MEH-PPV, MDMO-PPV, P3HT, and P3OT have been reported as electron donors in photovoltaic devices. In this research, we studied the use of a water soluble polythiophene - Sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate]) [PTEBS] in photovoltaic devices. Solar cells in the configuration of bilayer heterojunctions with TiO₂ were prepared. The water-soluble polythiophene showed significant photovoltaic effect and potential for use in solar cells. The use of this polymer would allow safe, environmentally friendly processing. In addition, due to the covalent bonding of the counterion to the polymer backbone chain simultaneously with electron loss in the doping and oxidation, the water-soluble polymer PTEBS can be self-doped by acids. The appearance and absorption spectra of the self-doped solutions and films have also been investigated. New absorption bands in the ultraviolet and infrared have been observed after acidic doping offering the possibility of improved light harvesting. Experimental results have shown that the polymer can be used as the active layer in photovoltaic applications. These photovoltaic devices had an energy conversion efficiency of 0.23% and a fill factor of 0.41 under the illumination of an 80 mW/cm² solar simulator. A simple mechanism has also been proposed to fit the open circuit voltage found in the devices.