The cost of platinum (Pt) counter electrode (CE) accounts for over 40% of the total cost of a dye sensitized solar cell (DSSC), thus replacing Pt with a cheaper material can significantly reduce the overall cost of the device. To this end, a novel cost-effective mesoporous carbon black (CB)/polyaniline nanotube (PAniNT) nanocomposite was fabricated as a potential CE material. The nanocomposite, prepared by chemical oxidation polymerization of aniline in the presence of CB, was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Different amount of CB were added in the polymer matrix to optimize the electro-catalytic activity of the CB/PAniNT nanocomposite towards reduction of I-3(-) to I-. Cyclic voltammetry, current density-voltage measurements, electrochemical impedance spectroscopy and Tafel plot analysis showed that incorporation of CB resulted in an augmented active catalytic surface area and enhanced charge transfer from CE to the electrolyte. These factors contributed towards achieving a high performance DSSC with efficiency of 6.62% in liquid electrolyte (LE) and 4.82% in polymethyl methacrylate based polymer gel electrolyte (PGE) under irradiation of light (100 mW cm(-2)). Furthermore, the effect of CE thickness was also studied in detail and the cell performance was found to improve proportionally with growing thickness. An optimized device was finally assembled with a 10.58 mu m thick 0.75 wt% CB/PAniNT nanocomposite film as CE corresponding to J(SC), V-0C and RCT values of 12.52 mA cm(-2), 0.74 V and 0.99 Omega for LE, and 9.11 mA cm(-2), 0.74 V and 1.30 Omega for PGE respectively. (c) 2017 Elsevier Ltd. All rights reserved.