Enhancing photovoltaic performances of dye-sensitized solar cells by multi-layered nanostructured titanium oxide photoelectrode

• A multi-layered photoelectrode comprising TiO2–MWCNT(1L)/P25-TiO2(6L) is fabricated.
• Cell efficiency enhances 27% as a multi-layered photoelectrode is employed.
• Excellent charge transport of MWCNTs is attributed to the enhancement in cell performance.
• The amount of dye loading was not influenced by the small amount of MWCNT additives.
• A compact sol–gel-deposited TiO2 blocking layer effectively suppresses the dark current.

In the present study, a multi-layered nanostructured titanium oxide film has been fabricated as the photoelectrode for dye-sensitized solar cells (DSSCs). The multi-layered TiO2 electrode has the advantages of easy fabrication, being compatible with current deposition process and readily modifiable by adjusting the process parameters. The application of TiO2–MWCNTs (multiwalled carbon nanotube) as a nanocomposite overlayer reduces the inhomogeneity of dispersing carbon nanotubes (CNTs) throughout the whole photoanode, which largely simplifies the fabrication process and improves the performance of the as-prepared photoanodes. By using a multi-layered photoelectrode comprising a structure of TiO2–MWCNT/Degussa P25-TiO2/compact TiO2/TCO glass, a 27% enhancement in conversion efficiency is realized in DSSC as compared with pristine P25-TiO2 photoanode of identical thickness. The enhancement in efficiency brought by incorporation of MWCNTs, as revealed by electrochemical impedance spectroscopy (EIS), could be attributed to the excellent charge transport properties of CNTs, which led to efficient charge transfer within nanoporous TiO2 networks. A compact TiO2 blocking layer suppresses effectively the dark current, thus enhancing both JSC and VOC prominently.