Direct extrapolation techniques on the energy band diagram of BiVO4 thin films

摘要

Bismuth vanadate (BiVO4) is one of the n-type semiconductors which has attracted attention as one of the promising photoanodes semiconductor for photoelectrochemical water splitting due to its small optical band gap, low cost, negative conduction band edge and good stability. In this work, BiVO4 thin films is fabricated by using electrodeposition method and the XRD spectra reveal that the sample crystallizes in monoclinic scheelite type. The optical bands show the bandgap energy of BiVO4 thin films is 2.40 eV as determined by Tauc plot and exhibits an anodic photocurrent. Further study is focusing on determination of the conduction band (CB) and valence band (VB) of BiVO4 thin films which is derived experimentally by using XPS analysis, Mott-Schottky plot and Cyclic Voltammetry (CV) technique. Based on the results, it is found that different analysis techniques exhibit almost similar values of CB and VB of BiVO4 thin films. All techniques give VB maximum in the range of 2.02 eV-2.05 eV and CB minimum in the range of 0.35 eV to 0.39 eV. However, the flat-band potential determined from Mott-Schottky plot is nearly 0.1 eV from CB potential caused by the presence of Fermi level and the effect of Helmholtz capacitance for dielectric semiconductors. These findings clearly show that the experimental values of different analysis techniques give comprehensive approach to understanding the energy band structure of the BiVO4 thin films.