Modified photoanodes by amino-containing phosphonate self-assembled monolayers to improve the efficiency of dye-sensitized solar cells

Abstract

Surface modification of TiO₂ electrodes by selected molecules could lower the energy barrier of electron transfer and improve DSSC performance. The category of the terminal group and molecular length of a self-assembled monolayer influence the surface and interfacial properties of a TiO₂ electrode, and the photovoltaic parameters of a DSSC could thereby be adjusted. By electrochemical approaches, it was discovered that the redox current and photocurrent increased when a lower work function and thus a reduced impedance at the TiO₂/dye/electrolyte interface were achieved by using an amino-containing phosphonic acid. However, a smaller photocurrent would be caused when the path for electron transport and charge recombination probability were increased by employing a longer molecule. Both the photocurrent and dark current of a DSSC were suppressed when a larger impedance restrained electron transport through the interface. The TiO₂ electrode modified by 2-aminoethylphosphonic acid showed the largest redox current. The corresponding DSSC exhibited the smallest impedance, largest photocurrent and highest efficiency of 6.67%. This study has demonstrated that a monolayer formed on the TiO₂ surface by an amino-containing phosphonic acid enhanced DSSC performance efficiently.