Highly catalytic cross-stacked superaligned carbon nanotube sheets for iodine-free dye-sensitized solar cells

Abstract

Searching for suitable platinum-free electrocatalysts toward novel iodine-free redox couples is of vital importance for further cost reduction and large-scale implementation of dye-sensitized solar cells (DSCs). Herein, cross-stacked superaligned carbon nanotube (CSCNT) sheets were incorporated as efficient economical cathodes in organic disulfide/thiolate redox electrolyte mediated DSCs. Electrochemical characterization revealed that the CSCNT sheets exhibited notably higher electrocatalytic activity toward the disulfide/thiolate redox shuttle over that of ubiquitous platinized cathodes, featuring a significantly decreased charge transfer resistance (ca. 1.26 Ω cm²) and a 4-fold attenuated apparent activation energy (ca. 6.90 kJ mol⁻¹) for disulfide reduction, as well as excellent electrochemical stability. Such a superior electrocatalytic activity was mainly attributed to the synergistic effect of the high specific surface area, relatively open structure for electrolyte accessibility and defect-rich CSCNT cathode. A device incorporating a CSCNT cathode confers a high fill factor of 0.67 and power conversion efficiencies up to 5.81%, which are significantly higher than 0.54 and 4.54% for that with a sputtered Pt cathode. Our investigations demonstrate not only the attractive feasibility of replacing scarce platinum cathodes with abundant carbon materials for novel iodine-free electrolytes, but also the importance of suitable catalyst redox coupling for progress in developing low-cost and high-efficiency DSCs.