Short communicationHigh-performance polypyrrole nanoparticles counter electrode for dye-sensitized solar cells
Introduction
Since the prototype of a dye-sensitized solar cell (DSSC) was reported in 1991 by O’Regan and Gratzel [1], it has aroused intensive interest over the past decade due to its low cost and simple preparation procedure [2], [3], [4], [5], [6]. In general, the DSSC has a sandwich structure with two transparent conductive glass substrates. The cell consists of an electrode composed of a porous nanocrystalline TiO2 film sensitized by a dye for absorbing visible light, a redox electrolyte, and a platinized counter electrode to collect electrons and catalyze I2/I− redox-coupled regeneration reaction in electrolyte. The principle of operation of the DSSC involves the photoexcitation of the sensitizer, followed by electron injection into the conduction band of the semiconductor oxide film. The dye molecule is regenerated by the redox system, which itself is regenerated at the counter electrode by electrons passing through the load.
Counter electrode of DSSC is usually made of platinum, which has high conductivity, stability and catalytic activity for I2 reduction. But platinum is one of the expensive components in DSSC [7]. Recently, to reduce the production cost of DSSC, porous carbon materials are attempted to replace platinum electrode, however, the conversion efficiency of the DSSC based on the carbon electrode is relatively low due to the poor catalytic activity for I2 reduction and lower conductivity of carbon [8], [9], [10], [11].
The conducting polymers are promising candidates as counter electrode materials used in DSSC, because of their unique properties, such as inexpensive, high conductivity, remarkable stabilities, good specific capacitances, and catalytic activity for I2 reduction [12], [13], [14], [15]. However, there are only a few reports on the conducting polymer as a counter electrode material using in DSSC. The polypyrrole (PPy) is one of the most intensively studied conducting polymers during the last decade. Beside its mechanical and chemical stability and high conductivity, polypyrrole is synthesized easily by electrochemical method in aqueous media [16], [17], [18]. Up to present, the polypyrrole has been employed to construct PPy/TiO2 anode or solid electrolyte used in DSSC, and the photoelectric performance of the DSSC was improved [19], [20], [21].
In this paper, the PPy nanoparticle was synthesized and coated on a conducting FTO glass to construct PPy counter electrode used in DSSC. It is expected that photoelectric performances of the DSSC with PPy electrode can be improved.
Section snippets
Synthesis of polypyrrole nanoparticle
The pyrrole monomer (Merck) used for the present study was purified by a vacuum distillation before using. All solvents were used without further treatment before using. All work was carried out in ambient atmosphere, unless specified otherwise. The PPy nanoparticle was synthesized as follows [22]. One gram of solid iodine was added into 200 mL of alcohol and distilled water solution with a volume ratio of 1:1. And then 1.5 mL of pyrrole (Py) monomer was added dropwise onto the surface of the
Morphology and compositions of polypyrrole
Fig. 1(a) shows the SEM image of polypyrrole nanoparticles prepared by 10 h ultrasonic irradiation in alcohol solution. It is clear that polypyrrole nanoparticles have been completely separated with a particle diameter of 40–60 nm. Fig. 1(b) shows the SEM image of PPy particles covered on the FTO glass with a magnification of 100,000 times. It can be seen clearly that PPy particles present in an diameter range of 40–60 nm on the FTO glass, and the surface exhibits porous state obviously, which
Conclusions
In summary, PPy nanoparticle was synthesized and coated on a conducting FTO glass to construct PPy counter electrode used in dye-sensitized solar cell. Scanning electron microscope images show that PPy with porous and particle diameter in 40–60 nm is covered on the FTO glass uniformly and tightly. Cyclic voltammograms of I2/I− system measurement reveals that the PPy electrode has smaller charge-transfer resistance and higher electrocatalytic activity for the I2/I− redox reaction than that Pt
Acknowledgements
The authors thank for the joint support by the National Natural Science Foundation of China (No. 50572030, 50372022), the Nano-Functional Materials Special Program of Fujian Province (No. 2005HZ01-4), the Key Project of Chinese Ministry of Education (No. 206074) and Specialized Research Fund for the Doctoral Program of Chinese Higher Education (No. 20060385001).
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