While purely optical spectroscopy can track efficiency-limiting loss mechanisms from film to the device, the extraction of charge carriers can only be properly analyzed in systems that feature two contacts and have the same degree of selectivity as the actual solar cell. Thus, there is a significant need for advanced characterization methods that are specifically applied to complete solar cells and that use electrical detection and electrical and/or optical excitation of the device. These methods can be performed in steady state, in the time- or in the frequency domain and often suffer from the superposition of a huge number of different physical effects that affect the outcome of the measurement. This leads to the challenge of solving the so-called inverse problem of extracting data from experiments.