Time resolved techniques such as transient photovoltage decay (TPV) [1], and frequency resolved measurements such as impedance spectroscopy (EIS) [2] and intensity-modulated photovoltage spectroscopy (IMVS) [3] are well established techniques that have increased our understanding of device operating physics in dye-sensitized solar cells (DSSCs) and have successfully been utilized as applied research tools for DSSCs [4]. The utilization of these techniques to characterize perovskite solar cells is beginning to keep pace with the rapid progress in perovskite technology but an understanding of observed phenomena, to the same degree as DSSCs, has yet to reach realization. Our understanding is complicated by the appearance of double exponential decays in the TPV data and observable processes in the order of tens of seconds, in both the time and frequency domain. In this presentation we will discuss results obtained from TPV and IMVS measurements. As both measurements are carried out at open-circuit and the perturbation is light driven, the result should be directly comparable and indeed this is what we observe. In cases where the TPV decay shows single exponential behavior, we see two features in the IMVS spectra. The high frequency region features an arc with an RC time constant that matches almost exactly to that obtained from the TPV decay. The low frequency IMVS arc is on a timescale much slower than that resolved in standard TPV measurements. Similarly, when a double exponential decay is observed in the TPV data, two high frequency arcs are distinguishable in the IMVS spectra. Again, the two RC time constants obtained from the IMVS arcs match those resolved from the TPV decay. Combining these techniques, we will show how the range of time constants relate to coupling between electronic and ionic effects on different time scales. Temperature dependent measurements help to show the impact of ion migration on these processes, and how they are linked to observable hysteresis in a variety of device architectures. We believe that the fastest time constants, observed on the microsecond time scale, relate to purely electronic processes without ionic redistribution. On longer timescales ions are able to migrate and influence the observed electronic behavior.

References:[1] B. C. O’Regan and F. Lenzmann, J. Phys. Chem. B, 2004, 108, 4342-4350[2] F. Fabregat-Santiago, et al., Sol. Energy Mater. Sol. Cells, 87 (2005) 117–131 [3] G. Schlichthörl, et al., J. Phys. Chem. B 1997, 101, 8141-8155 [4] M. J. Carnie et al., J. Mater. Chem. A, 2013, 1, 2225