The morphology and elemental composition of the prepared layers were initially determined using a Vega Surface photovoltage (SPV) measurements were performed with a Kelvin probe (Instytut Fotonowy) combined with a monochromator and a Xenon arc lamp (Instytut Fotonowy). An oscillating reference electrode made of a gold grid was used. The electrodes were contacted using copper tape. First, the contact potential difference (CPD) in the dark was measured over time to stabilize the sample. The SPV measurements were carried out under ambient conditions under intermittent monochromatic irradiation (320 s / 60 data points in the dark, 320 s / 60 data points under illumination) from 500 nm to 300 nm with a step of 20 nm.