Capacitance-Based Methods to Study Charge Transport and Recombination in Organic Solar Cells

In the last decades, organic photovoltaics has emerged as a promising environmentfriendlyand low-cost technology for the production of energy. Even though the efficiencyof organic solar cells has increased rapidly during the last years, further improvementsin terms of device lifetime and performance are still needed for a successfulcommercialization of such solar cells.In this work, two important processes affecting the efficiency of organic solar cells,namely the recombination and the transport of charge carriers, are investigated. Solution-processed solar cells based on different polymer:fullerene systems are studied byusing impedance-based techniques, specifically capacitance-voltage and capacitancefrequencymeasurements, in combination with steady state current-voltage measurementsand numerical simulations.In the first step, current-voltage measurements and drift-diffusion simulations areused together to develop a method to discriminate between surface and bulk recombinationin organic solar cells. The application of the method to a range of current-voltagedata of organic solar cells based on different polymer:fullerene systems and with diversearchitectures confirms the validity of the method and shows the possibility toobserve the whole range of cases, from mostly surface limited to purely bulk limitedrecombination, in the field of organic photovoltaics