Nitrogen doped carbon nanotubes grafted TiO2 rutile nanofilms: Promising material for dye sensitized solar cell application

Abstract

The TiO2 based solar cells are an exciting 3rd class generation photovoltaic, since they hold promise for the realization of large area devices that can be fabricated by room temperature solution processing, that can lead to high photoactive performance. Here, we reported similar efficiencies by focusing our work on obtaining sol-gel thin films belonging to N-CNT/TiO2 system by dispersing nitrogen doped carbon nanotubes (N-CNTs) powders in titanium tetra-isopropoxide using sol gel route. The film samples were evaluated in terms of structure morphology and optical properties using XRD analysis, atomic force microscopy (AFM) for TiO2, thin film scanning electron microscopy (SEM) for TiO2 and N-CNT/TiO2 thin films as well as UV–vis absorption spectroscopic techniques. X-ray diffraction analysis of films produced by the sol gel route and deposited on ITO glass has shown that they are also amorphous before annealing. However, XRD spectra showed only the peak of the rutile phase after the high annealing temperatures starting from 300 °C. The SEM micrographs showed the presence of grains of very small sizes, the grain size increases with the annealing temperature. The measurements made by AFM revealed that the thickness and roughness increase with the rise of annealing temperature of the film. 300 °C is the optimum temperature. This finding was assessed by the experimental investigation of annealing temperature effect through determination of specific area and pores diameter using BET and BJH methods respectively.Moreover, it was confirmed by SEM observations that the grains of N-CNT/TiO2 thin films are homogeneously dispersed and transmission electron microscopy clearly indicated that TiO2 grains are adsorbed on N-CNTs. Optical transmittance of N-CNT/TiO2 indicated a decrease with increasing the incorporated wt% N-CNTs. This behavior is due to charge carriers increase, which lead to band gap narrowing. The findings concerning the optical gap are assessed by electrical measurements. After careful analysis of the results presented in this work, we have deduced that the mentioned method is found to be simple and more efficient in the calculations of direct band gap.