Monoclinic bismuth vanadate band gap determination by photoelectrochemical spectroscopy

•Optical band gap of monoclinic BiVO4 was determined by photocurrent spectroscopy.•Indirect optical transitions are characterized by the energy Egi = 2.44 eV.•Direct optical transitions are characterized by the energy Egd = 2.63 eV.

The optical band gap (Eg) of the monoclinic bismuth vanadate BiVO4 (scheelite) was determined by photoelectrochemical (photocurrent) spectroscopy. The relevance of this study is related to an existing ambiguity in Eg determination, which is due to possible distinction in preparation technique of this compound (and, hence, difference in grain size, crystallinity, film thickness, etc.), as well as realization of additional optical absorption mechanisms unrelated to excitation of electrons from the valence band to the conduction band. Using analysis of the Incident Photon-to-current Conversion Efficiency (IPCE), which minimizes a contribution of impurity-related and other kinds of absorption, it was demonstrated that BiVO4 scheelite is primarily indirect band gap semiconductor, where indirect optical transitions are characterized by the energy gap Egi = 2.44 eV, whereas for direct optical transitions energy gap is Egd = 2.63 eV.