Thermal energy plays a crucial role on the phase evolution of niobium oxide (Nb2O5) thin films and when employed as a blocking layer these films can manoeuvre charge transfer process in a dye sensitized solar cell (DSSC). Niobium oxide film, prepared by RF magnetron sputtering process, endured phase transitions successively from amorphous to orthorhombic and finally to monoclinic phases when subjected to post-deposition annealing. The co-existence of orthorhombic and monoclinic phases with an interesting surface morphology is perceived at an annealing temperature of 900°C. Nb2O5 blocking layer at the FTO/TiO2 interface strongly influenced the photovoltaic parameters of the DSSC and the blocking layer in the orthorhombic phase is found to be most effective in suppressing charge recombination and delivered a maximum efficiency of 7.33%. The improvement in open circuit voltage can be foreseeable as shifting of the Fermi level towards the conduction band edge of the TiO2 as a result of structural modification of the Nb2O5 blocking layer. The thermal stability of the FTO is also investigated and found that the electrical and optical properties of FTO were remarkably stable up to 600°C and begin to change appreciably from 700°C onwards.
S. Suresh, Unni, G. E., Ni, C., R. Sreedharan, S., R. Krishnan, R., Satyanarayana, M., Shanmugam, M., and Pillai, V. P. Mahadevan, “Phase modification and morphological evolution in Nb2O5 thin films and its influence in dye- sensitized solar cells”, Applied Surface Science, vol. 419, pp. 720 - 732, 2017.