Influence of carbon nanotube wall thickness on performance of dye sensitized solar cell with hierarchical porous photoanode

• CNTs with different diameters are applied in dye sensitized solar cell.
• Medium acid functionalization of CNTs leads to the most stable dispersion.
• CNT with highest diameter (CNT-60) shows the best device performance.
• Higher dispersibility and chemical stability in CNT-60 cause proper performance.
• CNT-60 based device also shows suitable electrical and optical properties.

The effect of carbon nanotube (CNT) diameter on the efficiency of dye sensitized solar cell (DSC) with hierarchical porous photoanode is investigated. Three different kinds of CNTs including a single-wall CNT (SWCNT) and two different multi-wall CNTs (MWCNT) with outer diameters of 10 and 60 nm are incorporated in titania sol after surface functionalization. The DSCs are fabricated based on sol–gel induced phase separation synthesized photoanodes. The most stable colloid of CNTs in ethanolic titania sol is achieved in MWCNT with higher wall thickness. The more functional carboxylic groups, which can further assist the CNT/TiO2 attachment, could be detected in these CNTs. Impedance spectroscopy shows that the lowest series resistance is obtained in MWCNT incorporated DSC with higher diameter, which is far lower than that of SWCNT, MWCNT with low diameter, or without CNT cells. The 60 nm diameter CNT incorporated cell leads to higher efficiency compared to cells without CNT, with SWCNT, or 10 nm MWCNT due to its proper chemical stability, acceptable thermal stability, and appropriate electrical properties.

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