Category SOLAR CELLS – DYE-SENSITIZED DEVICES

Preparation of carbon nanofiber counter electrode

The carbon nanofiber paste was made by mixing 0.1 g ECNs with 19.6 g polyoxyethylene(12) tridecyl ether (POETE) in a similar method reported by others (Mei & Ouyang 2009). The mixture was then grinded, sonicated, and centrifuged at a spin speed of 10,000 rpm to uniformly disperse the ECNs in POETE. Any extra POETE that floated on top of the mixture after the centrifuge was removed via a pipette. Afterwards, the counter electrode was made by doctor-blading the mixture onto FTO (~8 Q/П and ~400 nm), followed by sintering at 200 °C for 15 min and then at 475 °C for 10 min. Figure 4 shows SEM and transmission electron microscope (TEM) images of the original carbon nanofibers prepared by electrospinning and the carbon nanofiber counter electrode on FTO deposited by doctor blading...

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Device performance of carbon/TiO2 composite counter electrode

The active area of carbon/TiO2 composite is 0.20 cm2, while that of Pt devices is 0.24 cm2. The slope of the straight line AB in carbon/TiO2 composite devices is 67.81 mA/ (cm2V), with a reciprocal of 14.75 Qcm2 . The slope of the straight line AB in Pt-based devices is 91.28 mA/(cm2V) and its reciprocal is 11.37 Qcm2. Apparently the series resistance of carbon/TiO2 devices is larger than that of Pt devices. This can be possibly attributed to the much thicker layer and larger resistivity of carbon/TiO2 counter electrode than those of Pt (Imoto et al. 2003). However, the carbon/TiO2 counter electrode has its own advantage that is the large surface area. This results in a lower Rct, which was found to be less than half of that in the Pt counter electrode (Ramasamy et al. 2007)...

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Calculation of series resistance, left justified

Ramasamy et al. measured the charge transfer resistance (Rct) of carbon electrode via electrochemical impedance spectroscopy (EIS) and found that Rct was 0.74 0 cm-2, two times less than that of the screen printed Pt (Ramasamy et al. 2007). Since the thickness of carbon – based counter electrode is tens of micrometers that are much higher than Pt at a thickness of about tens of nanometers, the internal series resistance (Rse) of carbon-based DSSCs are found to be higher (Ramasamy et al. 2007; Joshi et al. 2009). The lower Rct counterbalances the higher Rse of carbon-based device. The series resistance of carbon/TiO2 composite based DSSCs was also studied and compared with that of platinum-based devices under multiple light intensities.

Current density (Jsc) through the series resistance is...

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Preparation of carbon/TiO2

Carbon nanoparticles (Sigma-Aldrich) have a particle size < 50 nm and a surface area > 100 m2/g. The TiO2 paste was prepared by dispersing TiO2 nanoparticles (P25 Degussa, average size of 25 nm) into water. The carbon/TiO2 composite was made by mixing 650 mg carbon nanoparticles with 1 ml TiO2 colloid paste at a concentration of 20 wt%. Then 2 ml deionized (DI) water was added, followed by grinding and sonication. 1 ml Triton X-100 was added during grinding. The final paste was then spin coated onto a FTO glasses to form the counter electrode, followed by sintering at 2500 C for an hour.

The scanning electron microscopy (SEM) images of carbon/TiO2 composite and pure TiO2 nanoparticle films are shown in Figure 1a and b, respectively...

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Carbon/TiO2 composite as counter electrode

Low cost carbon/TiO2 composite was used as an alternative to platinum as a counter­electrode catalyst for tri-iodide reduction. In the carbon/TiO2 composite, carbon is nanoparticles and acts as an electrocatalyst for triiodide reduction, while the TiO2 functions as a binder. The carbon/TiO2 composite can be deposited by spin coating or doctor blading onto a fluorine-doped Tin Dioxide (FTO).

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Carbon Nanostructures as Low Cost Counter Electrode for Dye-Sensitized Solar Cells

Qiquan Qiao

South Dakota State University United States

1. Introduction

In the last two decades, dye sensitized solar cells (DSSCs) have gained extensive attention as a low cost alternative to conventional Si solar cells (Oregan & Gratzel 1991; Fan et al. 2008; Xie et al. 2009; Alibabaei et al. 2010; Gajjela et al. 2010; Xie et al. 2010; Yum et al. 2010). A typical DSSC is made of a TiO2 photoanode and a Pt counter electrode separated by an electrolyte comprising an iodide/triiodide (F/I3~) redox couple. The photoanode is usually prepared from TiO2 nanoparticles on a transparent conducting oxide (TCO), while the counter electrode is a thin layer of Pt deposited on another TCO substrate. The dye molecules are adsorbed onto TiO2 surface...

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Alternative dyes for ZnO

According to the limitations of ZnO based DSSC, the lower electron injection and the instability of ZnO in acidic dyes, the alternative type dyes will provide a new pathway for useage of ZnO nanomaterials as photoanodic materials for effective solar power conversion. The list of other alternative dyes were compiled and given in Table 4. The new types of dyes should overcome above mentioned two different limitations and it should be chemically bonded to the ZnO semiconductor for effective for light absorption in a broad wavelength range. Already few research groups were already developed with the aim of fulfilling these criteria. The various new types of dyes include heptamethine-cyanine dyes adsorbed on ZnO for absorption in the red/near-infrared (IR) region (Matsui et al...

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Limitation on ZnO-based DSSCs

Although ZnO possesses high electron mobility, low combination rate, good crystallization into an abundance of nanostructures and almost an equal band gap and band position as TiO2, the photoconversion efficiency of ZnO based DSSC still limited. The major reason for the lower performance in ZnO-based DSSCs may be explained by the a) formation of Zn2^>/dye complex in acidic dye and b) the slow electron-injection flow from dye to ZnO. Zn2^>/dye complex formation mainly occurs while ZnO is dipped inside the acidic dye solution for the dye adsorption for a long time. Ru based dye molecules consisits of carboxylic functional group for coordination, dye solution mostly existing in acidic medium. Therefore, the Zn2^>/dye complex is inevitable...

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