Lithium Incorporation into TiO₂ Photoanode for Performance Enhancement of Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are one of the most favorable solar cell technologies owing to their low cost and ease of fabrication. The electron transport layer, consisting of a mesoporous titanium oxide (TiO₂) photoanode, plays a crucial role in DSSCs. In this study, we performed a post-lithium (Li) treatment on TiO₂ films to enhance the optoelectronic features and power conversion efficiency (PCE) of DSSCs. The material properties of pristine and Li-treated TiO₂ films were examined by X-ray diffraction (XRD), atomic force microscopy (AFM), steady-state photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). Li treatment was confirmed to suppress defects and enhance the crystallinity of the TiO₂ films. Furthermore, TiO₂ films sensitized with N719 dye were used as photoanodes and Pt as a counter electrode for the fabrication of DSSCs. The devices with 0.1 M Li-TFSI treatment showed a performance improvement of ∼20%, with a PCE of 10.5%, while the control DSSC had a PCE of 8.7%. The device performance was significantly enhanced owing to improved structural properties, efficient charge transport, and suppression of recombination owing to the passivation of trap states.