Li@SWCNT and Cup-Stacked Carbon Nanotubes for Dye-Sensitezed Solar Cells

Carbon Nanotubes (CNTs) are extensively studied for energy applications, mainly as additives in composite electrodes to promote electric and thermal conductivity, reinforce the mechanical strength, and enhance the flexibility and performance. Also, introduction of this nanomaterial into the semiconductors electrodes can reduce the resistance of the active materials and produce a composite nanomaterial, due to the electronic interactions between carbon nanostructures and other nanomaterials or substrates.

The studies developed by our group are concentrating on the synthesis of doped carbon nanotubes having different pristine properties produced by CVD or arc-reactor methods for energy devices applications.

The synthesis of Li@SWCNT by arc-reactor method produced selectively metallic tubes, with wettability in water and polar solvents [1]. For Cup-stacked carbon nanotubes (CSCNT) synthetized by CVD method, the tubes present semiconductor properties, high defective structure and wettability too. Herein, we realized studies in photoanode and counter electrode for dye-sensitized solar cells (DSSC) about the use of these two CNTs due to their special properties.

The photovoltaic properties were characterized by photocurrent-voltage (J-V) curves under illumination and impedance spectroscopy in order to study the incorporation of CNTs effects in the photoanode (CSCNT) and counter electrode (Li@SWCNT).

The CSCNT presented better performance for photoanode in DSSC due to the semiconductor and defective structure that promotes better interaction between CSCNT and TiO₂ paste used to prepare the electrode. The addition of CSCNT in the concentration range 0.3 to 0.1 wt% (TiO₂ electrode doping with CSCNT) has positive effects on the efficiency of DSSC, like the increase of the photocurrent and the efficiency, further on the photoanode remains transparent. The best result was obtained for 0.26% wt% of CSCNT.

On the other hand, Li@SWCNT showed best results when used as counter electrode. This material showed the same behavior as platinum in impedance spectroscopy and was incorporated by spray method in the FTO glass substrate.

[1] Matsubara, E.Y.; Luengo, C.A. and J.M. Rosolen. Lithium-doped endohedral single-walled carbon nanotubes can arise during tube growth. Chemical Physics Letters 590, 175–179 (2013).