Photoelectrochemical cells (PEC) typically use water as electrolyte and semiconducting electrodes, which are able to absorb light at a certain wavelength. By generation of electron-hole pairs in such an electrode, which can in further consequence trigger an electrochemical reaction, the energy of light is converted into chemical energy by splitting water into hydrogen and oxygen. Typical photovoltaic (PV) cells use a semiconductor p-n junction to convert the photon energy into electrical energy.
Our research interest, however, is not in these classic PEC and PV cells, but in a new type of all-solid-state photoelectrochemical cell. In our cells, we use changes of the electrochemical potential under illumination to drive ions either through a material or across phase boundaries. By moving these charge carriers we can create voltages and currents which may be used for either generating electricity or for direct conversion of light into chemical energy in a cell, e.g. by splitting CO2 or water. As these cell types are completely new and constitute the basis of the newly emerging field of “photo-ionics”. Our research focus is on understanding the underlying processes of these photo-ionic effects. Important for this research topic are mixed ionic electronic conducting materials with suitable bandgaps.