Characterization of interfacial charge transport and recombination by impedance spectroscopy on SiO2 coated TiO2 based dye sensitized solar cells

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.