Contact-free photovoltage measurements of photoabsorbers using a Kelvin probe

A contact-free method to measure the photovoltage that can be generated by an absorber, upon illumination, is presented. The measurement is based on Kelvin’s well-known capacitor method which measures the contact potential difference that builds up between two sufficiently conducting materials of different work function that are electrically connected. We show that the photovoltage of an absorber, which is introduced into the Kelvin capacitor, can be measured accurately, even though it is not in electrical contact to any of the capacitor plates. Comparative measurements of the surface photovoltage of an n-type Si semiconductor surface in grounded and nongrounded mode as well as the interface photovoltage of mesoporous TiO2, deposited onto a conducting substrate, are presented to demonstrate the feasibility of the concept. This approach enables to measure the photovoltage of complete solar cells and also its single components (absorber, absorber + buffer layer, absorber + buffer layer + electron and∕or hol...