Abstract

Background: Until now various structures of photoanode are made by incorporating graphene in the photoanode structure and applying them in DSSCs. Literature review indicates that despite the considerable researches which are performed on the application of TiO₂/Graphene nanocomposites in DSSCs, there is still no prevailing acceptable explanation for origin of the better performance by graphene.

Methods: Here a TiO₂ paste with 20-30 nm particle sizes is deposited by doctor blade method. Graphene sheets are synthesized by the chemical methods and their properties are investigated by the Raman spectroscopy and atomic force microscopy techniques. TiO₂/Graphene nanocomposite photoanodes are made in four different types by chemical methods. Pt cathode layer is deposited on the FTO coated glass substrates by doctor blade method from a Pt paste. Photoanodes are sensitized by N₇₁₉ dye. The active area of the cells was 0.25 cm². Optical absorption of the photoanodes is investigated by Perkin-Elmer spectrophotometer. Morphology of the photoanodes is observed by scanning electron microscopy. Parameters of electron transport in the cells were measured by the electrochemical impedance spectroscopy (EIS).

Results: We have shown that in spite of the micron size of graphene sheets, their scattering properties are not considerable in dye sensitized solar cells. It is shown that graphene sheets enhance the electron recombination resistance in the cells noticeably. We have shown that the electron diffusion length is enhanced from 20.32 microns to 35.41 microns after incorporating graphene sheets in the photoanode architectures. In the present study, efficiency of the cells with the TiO₂ architecture (5.97 %) was improved to 6.46 % after incorporating graphene sheets in the photoanode architecture.

Conclusion: Graphene sheets enhance the efficiency of the cells by improving electron diffusion length in the photoanode structure. As a general conclusion, our results show that in spite of theoretical prediction of considerable electron transfer rate of graphene sheets, this property is not noticeable in DSSCs.

Keywords: Diffusion, dye, graphene, impedance spectroscopy, solar cell, sensitizer.

Graphical Abstract