Intensity-Modulated Photocurrent Spectroscopy for Solar Energy Conversion Devices: What Does a Negative Value Mean?

Small perturbation techniques constitute a wide family of tools for the characterization of solar energy conversion devices such as photovoltaic cells and photoelectrochemical (PEC) cells for solar fuel production. Two main small perturbation methods frequently used in the area of solar energy conversion materials are impedance spectroscopy (IS) and intensity-modulated photocurrent spectroscopy (IMPS). The first one consists of applying a small voltage perturbation and measuring modulated extracted current. The second one consists of applying the perturbation to the illumination and measuring the modulated extracted current.