Understanding the role of dielectric permittivity in charge transfer in organic materials
Poor performance in organic photovoltaics has often been accredited to the low dielectric function (< 5) of organic materials impacting on poor charge separation; it is therefore necessary to develop materials with high dielectric permittivity and investigate its effect on charge transfer processes. We will study organic semiconductors by performing optical spectroscopy from the visible to the far infrared range. The level of doping in the n or p organic layers will be monitored by FT-IR spectroscopy by looking at the charge sensitive vibrations, on which we have extensive experience based also on modelling and impedance spectroscopy. The process of charge separation will be monitored by heterodyne pump-probe spectroscopy from the 300 femtoseconds to 3 nanoseconds time scale. The spectroscopy studies will be aiming to explain what occurs in real devices and, therefore, after the first experiments the investigated structures will be more similar to solar cells with both transport layers and electrodes.