Characterization of BiVO4 powders and cold gas sprayed layers by surface photovoltage techniques

Abstract Electronic states in BiVO 4 powders and in cold gas sprayed BiVO 4 coatings were characterized by modulated and transient surface photovoltage (SPV) spectroscopy. The SPV signals measured in the spectral ranges between 2.2 and 2.5–2.6 eV and above 2.6 eV were negative and positive, respectively. Therefore, electrons (holes) photo-generated from defect states near the surface or photo-generated by fundamental absorption in the bulk were predominantly separated towards the bulk (surface) or towards the external surface (bulk), respectively. Bulk defect states dominating the modulated SPV signals between 1.8 and 2.2 eV were observed after cold gas spraying but disappeared after moderate post-annealing. Random walk simulations of SPV signals gave evidence for transport limitation by hopping for excitation from defect states.