Electrochemical investigation of PEDOT:PSS and Nb2O5 composites as counter electrodes for dye-sensitized solar cells

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has attracted considerable interest to replace expensive and rare platinum (Pt) in counter electrodes (CEs) of dye-sensitized solar cells (DSC). The use of niobium pentoxide (Nb2O5) combined with this polymer has not yet been reported. In the present paper, the DSC performance was compared with five different types of CEs Pt, PEDOT:PSS, PEDOT:PSS with Nb2O5 and Nb2O5 deposited via spin coating and doctor blading. For the characterization of the device, open-circuit voltage (Voc), short-circuit current density (Jsc), current density versus potential curves, electrochemical impedance spectroscopy (EIS), intensity-modulated photovoltage spectroscopy (IMVS), and intensity-modulated photocur-rent spectroscopy (IMPS) measurements were applied. The performance of DSC with CE of PEDOT:PSS (j = 4.59 +/- 0.70 mA cm-2; q = 0.89 +/- 0.19%) was significantly improved by the incorporation of Nb2O5 with photo -electrochemical parameters of j = 8.35 +/- 0.30 mA cm-2; q = 2.65 +/- 0.61%. This behavior is attributed to a reduction of the charge transfer resistance in the film as shown by EIS. The electron transport time was shorter for the PEDOT:PSS_Nb (Ltr = 0.002522 s) CE when compared to Pt standard counter electrode with a Ltr = 0.006336 s, but the electron lifetime was superior, which resulted in collection efficiency of qc = 84.15% when PEDOT:PSS_Nb was used.