Effect of Ni doping on the characterization of TiO2 nanoparticles for DSSC applications

Abstract

The photoanode junction in dye-sensitized solar cells (DSSC) must have low charge transfer resistance and high current density to enhance the cell efficiency. To improve these properties, nanostructured and doped TiO2 materials were tried, and in the present work, the transition metal ion (nickel) was doped into TiO2 and the cell performance was analyzed. Initially, undoped and Ni-doped TiO2 nanoparticles were synthesized by sol–gel technique with varying the concentration of nickel nitrate from 0.0 to 0.2 M (0.0 M: NT-0; 0.025 M: NT-1; 0.05 M: NT-2; 0.1 M: NT-3; 0.2 M: NT-4). The crystal structure, morphology, compositional, optical, and electrical properties were systematically analyzed, and the prepared photoanodes were used in DSSC. From XRD, the prepared samples exhibit the formation of a tetragonal crystal system with anatase phase and it was confirmed by micro-Raman analysis. The average crystallite size was found to vary from 10.54 to 5.37 nm when nickel molar concentration increases from 0.0 to 0.2 M. From FESEM analysis, the prepared nanoparticles were found to be spherical in shape and agglomerated in some places. The occurrence of only pure Ni, Ti, and O elements in EDS spectra confirmed the formation of pure Ni-doped TiO2 nanoparticles. From UV-DRS analysis, the optical absorption edge was red shifted and the corresponding band-gap energy was found to be decreased from 3.0 to 2.21 eV with increasing the Ni molar concentrations from 0.0 to 0.2 M. The PL analysis confirms that band–band PL emission, band-edge free excitons, bound excitons, and oxygen vacancies. DSSCs were fabricated using prepared photoanodes (NT-0 to NT-4), N719 dye, LiI/I as electrolyte, and platinum (Pt) counter electrodes. The charge transfer resistance (Rct2) of NT-4 was found to be 72.8 Ω, and it has a low resistance value which was calculated from the electrochemical impedance spectroscopic analysis. The overall photoconversion efficiency of Ni-doped TiO2 (NT-4) was found to be 3.60% which was comparatively higher than the other cells and undoped ones.