With the aim of introduction a new inexpensive co-adsorbent to improve solar cell performance, the influence of nicotinic acid (NTA) used as a co-adsorbent in dye-sensitized solar cells (DSCs) was investigated. The findings showed that low concentrations of NTA (< 10 mM) increased the N719 ruthenium dye loading on the TiO2 electrode surface by 10-12%, whereas higher concentrations of NTA lowered the dye loading. The adsorption of NTA onto the TiO2 electrode surface was studied by attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, and the blocking effect of NTA toward electron transfer between the electrode and 1,4-dicyanonaphthalene (redox couple electrolyte probe) was investigated by cyclic voltammetry. Subsequently, the performance of NTA in functional DSCs was evaluated by current-voltage (J-V) DSC characterization and compared with that of DSCs fabricated with two well-established co-adsorbents i.e., chenodeoxycholic acid (CDA) and octadecylphosphonic acid (OPA). The findings showed that under optimized co-adsorbent concentration (1 mM NTA, 0.03 mM CDA, 0.015 mM OPA), the efficiency of the corresponding solar cells increased to the same extent. Specifically, the use of NTA at optimum concentration improved the efficiency of the resulting DSC from 3.14 to 5.02%. (C) 2016 Elsevier B.V. All rights reserved.