INFLUÊNCIA DO Nb2O5 EM CÉLULAS SOLARES FOTOVOLTAICAS A BASE DE ZnO

Abstract

Investment in renewable energy sources has increased in recent decades due to the high environmental impact generated by the use of non-renewable sources. In this context, the conversion of solar energy into electric energy is quite promising. Dye sensitized solar cells (DSSCs) show as a promising alternative, since they are simple, non-toxic and have relatively high efficiency, but still present losses in the energy conversion process due to the effects of electronic recombination at the cell interfaces. Zinc oxide (ZnO) has been used as an electron acceptor in this type of cell because it offers good electron transport properties. In order to reduce the effects of charge recombination, niobium oxide (Nb2O5) was used, which can provide an energy barrier due to its higher energy gap when compared to other semiconductors. The zinc oxide used was commercially available and the niobium oxide was prepared by the Pechini methodology. The oxides were characterized by X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). A mixture of the oxides in the proportions of 1, 5, 10 and 15% m/m of niobium oxide in zinc oxide was prepared. The mixtures were analyzed by XRD techniques, where it was observed that zinc oxide retained its structure after addition of Nb2O5 and the addition of niobium oxide was confirmed by the technique of X-ray Fluorescence Spectroscopy. The films obtained were evaluated by open circuit voltage (Voc) and photocronoamperometry where the cells were light sensitive, the efficiency was calculated, and the cell containing 1% and 5% of niobium presented the best Efficiencies ɳ = 1.35% and 1.42%, respectively. In the electrochemical impedance spectroscopy (EIS) technique the time constants for Nb2O5 containing cells were shifted to lower frequencies indicating that the recombination reactions are slower. The results of curves of Photocurrent Spectroscopy with Modulated Intensity and Photovoltage Spectroscopy with Modulated Intensity showed that the efficiency of electronic collection was higher for the cell with 5% of niobium.