Interpreting the impedance response of perovskite solar cells is significantly more challenging than for most other photovoltaics. Here we provide a way to obtain useful information from the spectrum using insights from drift-diffusion simulation.

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Hybrid metal halide perovskites are mixed ionic-electronic semiconductors with exceptional optoelectronic properties, ideal for applications in photovoltaics, [1][2][3] lighting, [4] lasing, [5] X-ray detection, [6] among others. In all these applications, robustness and stability of the material are crucial. Bearing in mind that perovskites are ionic materials, it is expected that ion migration plays a significant role in all stability issues under operational conditions that often are triggered by irreversible ionic displacements. [7] The mixed ionic-electronic nature of metal halide perovskites was first described by Eames and co-workers in 2015. [8] Mobile ion defects have been widely acknowledged to influence charge transport in perovskite solar cells (PSCs) through generation of an electrostatic field profile that partially screens the field due to the applied bias and built-in voltage. [9,10] One of the most studied manifestations of ion migration in PSC is current-voltage hysteresis.

Recombination mechanisms in solar cells are frequently assessed through the determination of ideality factors. In this work we report an abrupt change of the value of the “apparent” ideality factor (nAP) in high‐efficiency FA0.71MA0.29PbI2.9Br0.1 based mesoscopic perovskite solar cells as a function of light intensity. This change is manifested as a transition from a regime characterized by nAP∼1.8–2.5 at low light intensities (<10 mWcm‐2) to one characterized by nAP∼1. This transition is equally observed in the recombination resistance extracted from open‐circuit impedance measurements. We use drift‐diffusion simulations with explicit consideration of ion migration to determine the origin of this transition. We find that a change ofrecombination mechanism concurrent with a modification of the concentration of ionic vacancies is the most likely explanation of the observed behaviour. In the drift‐diffusion simulations we show that the apparent ideality factor is in fact affected by the ion vacancy concentration so it is not the optimal parameter to assess the dominant recombination mechanism. We argue that a procedure based on a recently derived “electronic” ideality factor obtained from the high frequency feature of the impedance spectrum is better suited to determine the recombination route that dictates the photovoltage.

The second generation of the open-source MATLAB-based software tool , for solving drift–diffusion models of charge transport in planar perovskite solar cells, is presented here. This version is based upon a generalisation of the original drift–diffusion model of charge carrier and ion motion in the perosvkite cell, as described in Courtier (J Comput Electron 18:1435–1449, 2019). The generalised model has the flexibility to capture (1) non-Boltzmann statistics of charge carriers in the transport layers, (2) steric effects for the ions in the perovskite layer, (3) generation of charge carriers from light made up of a spectrum of different wavelengths and, (4) Auger recombination. The updated software is significantly more stable than the original version and also adds the ability to simulate impedance spectroscopy measurements as well as transient voltage and/or illumination protocols. In addition, it is fully backwards compatible with the original version and displays improved performance through refinement of the underlying numerical methods. Furthermore, the software has been made accessible to a wider user base by the addition of , a version that leverages MATLAB’s live scripts and eliminates the need for a detailed knowledge of MATLAB’s syntax.