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Research Papers

# Improved Efficiency of Dye-Sensitized Solar Cells Using a Vertically Aligned Carbon Nanotube Counter Electrode

[+] Author and Article Information
Robert A. Sayer, Stephen L. Hodson, Timothy S. Fisher

School of Mechanical Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907

J. Sol. Energy Eng 132(2), 021007 (May 06, 2010) (4 pages) doi:10.1115/1.4001148 History: Received September 06, 2009; Revised December 10, 2009; Published May 06, 2010; Online May 06, 2010

## Abstract

Dye-sensitized solar cells (DSSCs) offer many advantages in comparison to their Si-based counterparts, including lower cost of raw materials, faster manufacturing time, and the ability to be integrated with flexible substrates. Although many advances have been made in DSSC fabrication over recent years, their efficiency remains lower than commercially available Si photovoltaic cells. Here we report improved efficiency of $TiO2/anthocyanin$ dye solar cell using vertically aligned arrays of carbon nanotubes (CNTs) as a counter electrode. Dense vertically oriented CNT arrays are grown directly on the counter electrode using microwave plasma chemical vapor deposition and a trilayer (Ti/Al/Fe) catalyst. The resulting arrays are $30 μm$ in height and have a number density of approximately $5×108/mm2$. By directly growing the CNTs on the counter electrode substrate, electrical interface conductance is enhanced. The performance of both as-grown and N-doped (using a nitrogen plasma) CNT arrays is reported. The fabricated DSSCs are tested under AM1.5 light. Increased short-circuit current is observed in comparison to graphite and Pt counter electrodes. We attribute this improvement to the large surface area created by the 3D structure of the arrays in comparison to the planar geometry of the graphite and Pt electrodes, as well as the excellent electrical properties of the CNTs.

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## Figures

Figure 1

(a) Illustration of a typical DSSC. (b) Schematic of charge transport in DSSCs (CB=conduction band; VB=valence band).

Figure 2

(a) Transmittance of the FTO coated glass slide. FESEM images of (b) individual TiO2 particles, (c) the TiO2 film, and (d) the MWCNT covered counter electrode. (e) The fully assembled DSSC.

Figure 3

(a) XPS data for MWCNTs grown with the flow rate of N2=0, 10, 25, and 50 SCCM and (b) corresponding N concentrations in the MWCNTs.

Figure 4

(a) J-V characteristics and (b) power density of DSSCs with different counter electrodes. All DSSCs were illuminated under 80 mW/cm2 AM 1.5 light.

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