Influences of polymerization time on structure and properties of polyaniline counter electrodes in dye-sensitized solar cells

Abstract

SO2-4 doped polyaniline (PANI) counter electrodes (CEs) on fluorine-doped tin oxide (FTO) glass substrates were fabricated, using electrochemical method under constant bias for different polymerization time. The effect of polymerization time on surface morphology, structure (such as doping level, conjugation and oxidization state), and electrocatalytic activity for I-/I-3 redox reaction of the obtained PANI CEs was investigated by scanning electron microscopy (SEM), UV-Vis absorption spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). SEM results indicated that the growth of PANI films on FTO substrate occurred in two phases. Properly increasing polymerization time could increase the specific surface area of PANI CEs, affording more electrocatalytic sites for the I-/I-3 redox reaction. Meanwhile, the conductivity of the PANI CEs increased gradually because of enhanced conjugation, emeraldine base (EB) structure, and SO2-4 doping degree. If the polymerization time was too long, however, the CE conductivity would decrease due to the formation of a thick film and superabundance of oxidized structure, resulting in an increase in the electron transfer resistance and decrease in the electrocatalytic activity of PANI CEs for I-/I-3 redox reaction. Dye-sensitized solar cells (DSSCs) based on PANI CEs with a polymerization time of 300 s and D149 dye showed the best photovoltaic performance, with a solar-to-energy conversion efficiency of 5.30%. This result is approximately 88% of the efficiency of Pt CE based-solar cells, suggesting that PANI CEs polymerized with electrochemical method may replace Pt CEs in DSSCs. © Editorial office of Acta Physico-Chimica Sinica.