Effect of thiourea incorporation in the electrolyte on the photovoltaic performance of the DSSC sensitized with pyridyl functionalized porphyrin

Abstract

In this study, we investigate the effect of a thiourea containing electrolyte on the photovoltaic response of a dye sensitized solar cell (DSSC) that is based on an A3B-type meso substituted porphyrin (where A and B are methyl-benzoate and phenylethynyl-pyridine, as electron acceptor and anchoring groups, respectively). A significant increase in the short circuit photocurrent (Jsc) of the solar cell is observed (from 9.38mA/cm2 to 11.93mA/cm2), which is attributed to a positive shift of the TiO2 conduction band (CB) edge and to a decrease in the charge recombination rate. The short circuit photocurrent Jsc dependence on the illumination intensity Pin and its reduction in dark current confirm that the increased electron injection efficiency is due to the positive shift in the TiO2 CB edge and suppression of the back charge recombination of injected electrons. The charge recombination retardation has been attributed to chemisorbed thiourea cations on the TiO2 surface, as confirmed by UV–vis absorption spectra and XRD patterns of the pure and thiourea doped TiO2 films. Electrochemical impedance spectroscopy (EIS) results indicate that the chemisorbed on the TiO2 surface thiourea cations might passivate the surface recombination sites and enhance the electron lifetime in the nanostructured TiO2 film, resulting in a slight improvement of the open circuit voltage (Voc) of the solar cell, in spite of the positive shift of the thiourea containing electrolyte CB edge. The overall power conversion efficiency (PCE) of the DSSC based on thiourea containing electrolyte (E2) is 5.34%, which is higher than the corresponding DSSC without thiourea electrolyte (E1) (3.36%), under identical conditions.