Hierarchical porous titania/carbon nanotube nanocomposite photoanode synthesized by controlled phase separation for dye sensitized solar cell

Abstract

Incorporation of carbon nanotubes (CNT) in titania photoanode of dye sensitized solar cell (DSC) with hierarchical porous structure synthesized by controlled phase separation was studied. The hierarchical porous composite photoanode contained mesopores of 15nm and macropores of 280nm with surface roughness of about 15.4nm. The Raman spectroscopy confirmed the presence of CNTs beside titania anatase phase. Also, the transmission electron microscopy revealed that a very thin titania layer was formed on CNTs after impregnation with titania sol. The I–V characteristics of the DSCs with and without CNTs showed that incorporation of CNTs in photoanode led to an increase in current density and efficiency, which was due to the increase in surface area and hence dye adsorption, increase in density of states in titania and charge injection, and increase in charge collection and electron lifetime. The electrochemical impedance spectroscopy exhibited lower series resistance, lower charge injection resistance, and higher electron lifetime in DSCs containing CNTs. Addition of CNTs in photoanode also affected the critical thickness of porous layer with which the maximum efficiency could be obtained. Furthermore, the open circuit voltage and fill factor of the DSCs was independent of thickness when TiO2/CNT composite was used. The optimum amount of CNTs was found to be 0.32wt%, which led to the short circuit current density of 10.12mA/cm2, open circuit voltage of 680mV, fill factor of 56%, and efficiency of 3.85%.