Theory of Impedance Spectroscopy of Ambipolar Solar Cells with Trap-Mediated Recombination

The analysis of recombination in solar cells suggests in many cases the presence of trap-mediated recombination in the absorber. We present a theory of the recombination of electrons and holes, the Shockley–Read–Hall model, using the impedance spectroscopy technique. We derive the impedance functions and the corresponding equivalent circuit model. After examining some cases of interest, we show that two semicircles can be obtained in the recombination circuit only if the chemical capacitance associated with traps is substantially larger than the chemical capacitances of free electrons and holes in the absorber bands, while in the other cases the normal behavior of one recombination arc will be obtained.