Nanocrystalline sol-gel Nb2O5 coatings : preparation, characterisation and application to photovoltaic cell, lithium battery and electrochromic device

Abstract

Thick and thin films of Nb2O5 have been prepared by the sol-gel process using cheap niobium pentachloride as precursor and a new synthesis route. The microstructure of the films was tailored by adding poly(ethylene glycol) (PEG) and carbon soot into the sol and varying the sintering temperature. The thesis describes the properties of the sols and their influence on the properties of the resulting nanocrystalline Nb2O5 films as electrodes in dye sensitised solar cells, electrochromic devices and rechargeable lithium batteries. A solar light-to-electric conversion efficiency of Ru(II) sensitised Nb2O5 solar cell as high as 7% under 120W/m² illumination was obtained. An equivalent electric circuit of the dye sensitised electrode/electrolyte interface based on the electrochemical impedance spectroscopy was modelled and found to fit all the results. The values obtained for the electric elements from the simulation of the results were found to relate material parameters to the cell performance and their influence on the cell performance are illustrated. The electrochromism and Li+-charge and discharge of the Nb2O5 films exhibited also good performance.