Fabrication and photovoltaic performance of counter electrode of 3D porous carbon composite

Abstract

Dye-sensitized solar cell (DSSC) has been widely investigated due to its low cost, simple fabrication process, and excellent photoelectric conversion efficiency. Generally, the DSSC is composed of photoanode, electrolyte and counter electrode. At present, platinum (Pt) film delivers the highest photoelectric conversion efficiency in the available counter electrode materials. However, Pt film is very expensive and prepared by relatively complicated and high-cost magnetron sputtering, which seriously hinders the large-scale applications in DSSC. Therefore, it is of highly academic and engineering significance to develop novel counter electrode materials with low cost and high photoelectric conversion efficiency to replace expensive Pt counter electrode. Previous research shows that carbon-based nanomaterials such as graphene and carbon nanotubes ard promising to be used as highly efficient counter electrode materials. However, the high-cost and complicated fabrication process restrict their practical applications in DSSC. To address such issues, here in this work, we present and fabricate a highly efficient and low-cost three-dimensional porous carbon composite, which is constructed by the relatively dense and conductive graphite film as bottom layer (PC layer), and the porous carbon nanoparticle film as top layer (CC layer). Our fabricated DSSC consists of commercial TiO<sub>2</sub> photoanode (m 4 mm×4 mm), and PC, CC, CC/PC composite, or Pt counter electrode with a size of m 8 mm×8 mm. The results show that under illumination (100 mW/cm<sup>2</sup>) provided by a solar simulator, the short circuit current densities (open circuit voltages) of DSSCs with PC, CC, CC/PC, and Pt counter electrodes are 11.45 mA/cm<sup>2</sup> (0.72 V), 11.88 mA/cm<sup>2</sup> (0.73 V), 12.00 mA/cm<sup>2</sup> (0.75 V), and 13.46 mA/cm<sup>2</sup> (0.74 V), respectively. The filling factors of DSSCs with PC, CC, and CC/PC are 56.09%, 59.80%, 65.28%, and 62.69%, respectively; the photoelectric conversion efficiencies of DSSCs with PC, CC, and CC/PC are 4.61%, 5.20%, 5.90%, and 6.26%, respectively. It is noted that compared with CC layer or PC layer counter electrode, the CC/PC counter electrode delivers better photovoltaic performance. Particularly, the filling factor of DSSC with CC/PC (65.28%) is even 4.10% higher than that of DSSC with commercial Pt (62.69%), and the photoelectric conversion efficiency of the CC/PC-based DSSC is as large as 5.90%, which reaches 94.2% of the Pt-based DSSC (6.26%). The excellent performance of DSSC with CC/PC counter electrode is attributed to the unique three-dimensional porous structure, which can not only facilitate the transfer of electrons and ions, but also provide abundant catalytic sites; these synergistic effects greatly enhance the photovoltaic conversion performance of CC/PC-based DSSC.