High-performance dye-sensitized solar cells with gel-coated binder-free carbon nanotubefilms as counter electrode

Abstract

High-performance dye-sensitized solar cells (DSCs) with binder-free films of carbonnanotubes (CNTs), including single-walled CNTs (SWCNTs) and multi-walled CNTs(MWCNTs), as the counter electrode are reported. The CNT films were fabricated bycoating gels, which were prepared by dispersing CNTs in low-molecular-weightpoly(ethylene glycol) (PEG) through mechanical grinding and subsequent ultrasonication,on fluorine tin oxide (FTO) glass. PEG was removed from the CNT films through heating.These binder-free CNT films were rough and exhibited good adhesion to substrates.They were used as the counter electrode of DSCs. The DSCs with SWCNT orMWCNT counter electrodes exhibited a light-to-electricity conversion efficiencycomparable with that with the conventional platinum (Pt) counter electrode, whenthe devices were tested immediately after device fabrication. The DSCs with anSWCNT counter electrode exhibited good stability in photovoltaic performance. Theefficiency did not decrease after four weeks. On the other hand, DSCs with theMWCNT or Pt counter electrode exhibited a remarkable decrease in the photovoltaicefficiency after four weeks. The high photovoltaic performance of these DSCs isrelated to the excellent electrochemical catalysis of CNTs on the redox of theiodide/triiodide pair, as revealed by the cyclic voltammetry and ac impedancespectroscopy.