Straightforward prediction of the Ni1-xO layers stoichiometry by using optical and electrochemical measurements
Résumé
In this study, we propose a straightforward method for x determination in sub-stoichiometric nickel oxide (Ni1−x O) films prepared by ultrasonic spray pyrolysis on fluor-tin oxide (FTO) substrates by varying the post-deposition thermal treatment. The Ni3+ concentration, the flat band potential (Φfb) and the open circuit potential (V oc) were determined by electrochemical impedance analysis in aqueous media and correlated to the transmission of Ni1−x O films. An x-ray photoelectron spectroscopy study was also performed to quantify the amount of Ni3+ in the films and compare it with the one determined by electrochemical analysis. The electrochromic behavior of the Ni1−x O films in non-aqueous electrolyte was investigated as well.
With increasing Ni3+ concentration the films became more brownish and more conductive, both V oc and Φfb values increased. Calibration curves of transmission at 550 nm or open circuit potential versus carrier concentration were plotted and allowed the prediction of x in an unknown Ni1−x O sample. The Ni1−x O films characterized by the highest Ni3+ concentration have a darker colored state but lower transmission modulation, due to their reduced specific surface and increased crystallinity.
Domaines
Matériaux
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