Extracting in Situ Charge Carrier Diffusion Parameters in Perovskite Solar Cells with Light Modulated Techniques

Frequency resolved methods are widely used to determine device properties of perovskite solar cells. However, obtaining the electronic parameters for diffusion and recombination by impedance spectroscopy has been so far elusive, since the measured spectra do not present the diffusion of electrons. Here we show that intensity modulated photocurrent spectroscopy (IMPS) displays a high frequency spiraling feature determined by the diffusion-recombination constants, under conditions of generation of carriers far from the collecting contact. We present models and experiments in two different configurations: the standard sandwich-contacts solar cell device and the quasi-interdigitated back-contact (QIBC) device for lateral long-range diffusion. The results of the measurements produce the hole diffusion coefficient of D-p = 0.029 cm(2)/s and lifetime of tau(p) = 16 mu s for one cell and D-p = 0.76 cm(2)/s and tau(p) = 1.6 mu s for the other. The analysis in the frequency domain is effective to separate the carrier diffusion (at high frequency) from the ionic contact phenomena at a low frequency. This result opens the way for a systematic determination of transport and recombination features in a variety of operando conditions.

Automated summary

Frequency resolved methods are widely used to determine device properties of perovskite solar cells. Obtaining electronic parameters for diffusion and recombination by impedance spectroscopy has been elusive, but intensity modulated photocurrent spectroscopy displays a high frequency spiraling feature determined by diffusion-recombination constants. Analysis in the frequency domain effectively separates carrier diffusion at high frequency from ionic contact phenomena at low frequency, leading to a systematic determination of transport and recombination features in operando conditions.