Effects of surface-modified photoelectrode on the power conversion efficiency of dye-sensitized solar cells

The effects of Na₂SO₄ as a surface modification material on the performance of dye-sensitized solar cells (DSSCs) were studied. The surfaces of TiO₂ films were firstly modified with aqueous Na₂SO₄ solution by a dip coating process, and then the resulting electrode was applied to the photoelectrode of a DSSC. The DSSC with the Na₂SO₄-modified photoelectrode had a power conversion efficiency of 9.01% compared with that (7.97%) of the reference cell, which corresponds to an increase of about 13.0% in the efficiency due to an enhancement in short-circuit current (J _sc ) and open-circuit voltage (V _oc ). A series of measurements such as UV-visible absorption, electrochemical impedance, incident photon to current conversion (IPCE) efficiency and dark current revealed that incorporation of Na₂SO₄ onto the TiO₂ film led to an increase of dye adsorption and a longer lifetime of electrons injected from dyes to the TiO₂ electrodes, resulting in the improvement in both J _sc and V _oc , compared to those of a reference device without surface modification.