Interfacial modification of the working electrode of dye-sensitized solar cells to improve the charge transport properties

Abstract

In this work, we demonstrate the importance of the interface between FTO and TiO₂ on the performance of dye-sensitized solar cells (DSSCs), and carried out the modification on such an interface by utilizing self-assembled monolayers (SAMs) with multiple carboxylic acid functional groups. The SAMs were passivated on the FTO electrode surface prior to the fabrication of the TiO₂ absorption layer. Charge transfer through the FTO/TiO₂ junction after the SAM modification process was shown to be improved compared to the pristine device interface without SAM modification. Careful investigation indicated that the extreme hydrophilic nature of the SAMs fabricated on FTO and the possible chemical interaction between the SAMs and TiO₂ facilitated the TiO₂ initial layer to be more compact and crystalline in nature, resulting in a decrease of the impedance and an increase of the electron mobility in the FTO/TiO₂ junction. Thus, the photocurrent and the overall conversion efficiency of the DSSCs was increased. The largest improvement in the cell conversion efficiency was from 7.7% to 9.1% under AM1.5G (1 sun).