Aim
Photocatalytic materials such as BiVO4 are of great interest, for example, for water splitting. Electronic defect states and surface passivation are important limiting factors. Photocatalytic materials can be applied as powders, porous layers or thin films what makes a simple and contactless photoelectric characterization of such materials still challenging.
Solution
SPV spectroscopy in the dc (Kelvin probe, measurement of the contact potential difference: DCPD) and ac (modulated) modes is a contactless and highly sensitive method allowing to detect very low SPV signals related to charge separation under excitation of defect states for powder, porous and thin film samples [1].
Application example
Figure 1 shows spectra of the modulated SPV amplitude for a BiVO4 thin film, porous layer and powder (see also [2]). The onset of the band gap of BiVO4 (2.5 eV), the energy parameters of exponential tails and transitions related to defects can be well measured. Figure 2 shows DCPD spectra of porous BiVO4 layers decorated with V13O15 with and without a passivating cobalt phosphate (Co-Pi) cocatalyst (see also [3]).
