Microwave-plasma surface modification of nanostructured-polyaniline:graphite composite counter electrode in dye-sensitized solar cells

Abstract

This work demonstrates microwave plasma surface modifications of nanostructured polyaniline (NPES)-based counter electrodes (CE). Oxidative oxygen (O2) plasma and reductive hydrogen (H2) plasma were used in this study. Optical emission spectra confirm the presence of reactive species in both plasmas through the emissive species, such as O2+, O+, O•, H(nl), and H2 Fulcher-α. Microwave plasma treatment does not affect the surface morphology of NPES composite CE, which conserves its granule nanostructures, as revealed by SEM. The water contact angle measurements demonstrate how the O2 plasma treatment improves surface hydrophilicity, contrary to the H2 plasma treatment. Raman spectroscopy results show significant changes in the intrinsic-oxidation state and the number of semiquinonoid species (SQ) of NPES after plasma treatments, which are represented by the ratios of Raman intensity at 1368–1260 cm−1 and 1624–1583 cm−1, respectively. Generally, O2 plasma treatment increases the intrinsic-oxidation state and SQ number, opposite to the H2 plasma. The optimum condition of microwave plasma-assisted surface modification was attained in one minute of O2 plasma treatment, producing NPES with the highest intrinsic-oxidation state and SQ number. A power conversion efficiency of 3.17 % was obtained by a dye-sensitized solar cell fabricated with a modified CE using a one-minute O2 plasma treatment.