Evolution of charge collection separation efficiencies in dye-sensitized solar cells upon aging: A case study

Abstract

j-V characteristics, electrochemical impedance spectroscopy (EIS) and spectral incident photon-to-current efficiency (IPCE) were monitored for dye-sensitized solar cells (DSCs) employing different electrolyte compositions (0.1 M I2 and either 2 M LiI or 1 M PMII and 2 M LiTFSI) under a range of different conditions (e.g. incident light intensity, electrical bias) over one month. Specifically, differential IPCE and electrochemical impedance spectroscopy (EIS) measurements were made consecutively under similar conditions (illuminated by 530627 nm light, near open-circuit). The performance of all cells increased with time, which was ascribed to a large increase in V oc, without a large concomitant decrease is jsc. This increase in Voc was attributed to a gradual upward shift of the TiO2 conduction band edge, which was validated by trends in R t,0 and C,0 values obtained from EIS that were consistent with all other aging trends. It was also found that the apparent charge separation efficiency, probably the dye regeneration efficiency, played an important role in the DSCs' performance. Although no standard aging protocol was followed in this study, the pseudo-aging' test here represents the first attempt to de-convolute various kinetic processes upon prolonged aging, and has provided new insights into device operation. © 2011 The Electrochemical Society.