Characterization of interfacial charge transport and recombination by impedance spectroscopy on SiO<inf>2</inf> coated TiO<inf>2</inf> based dye sensitized solar cells

Abstract

Performance of dye sensitized solar cells (DSSCs) was improved 80%, by treating the mesoporous titanium dioxide (TiO 2 ) surface using atomic layer deposited (ALD) ultra thin silicon dioxide (SiO 2 ), compared to a DSSC with untreated mesoporous TiO 2 photoelectrode. Effect of SiO 2 treatment on charge transport, recombination and lifetime of electrons in the TiO 2 were investigated by electrochemical impedance spectroscopy (EIS). X-ray photoelectron spectroscopy confirmed the ultra thin growth of SiO 2 on the surface of mesoporous TiO 2 . Dark current-voltage (I-V) characteristics of the DSSCs with SiO 2 surface treatment showed that the TiO 2 /electrolyte interface quality was better than that of DSSC with untreated mesoporous TiO 2 in terms of defect density. Photovoltaic performance of the DSSC which used SiO 2 surface treatment showed that the effect of reverse electron recombination was significantly suppressed compared to the DSSC which did not use SiO 2 treatment. Dark and illuminated I-V measurements of the DSSCs which used SiO 2 surface treatment suggested that the lower thickness of SiO 2 (5 cycles) did not block electron transport from the dye to TiO 2 but thicker SiO 2 (20 cycles) blocked but still the performance was better than the DSSC with no SiO 2 treatment due to the control on density and activity of TiO 2 surface states on electron transport.