Impedance spectroscopy offers access to all the different electronic/ionic processes taking place simultaneously in an operating solar cell. So far, its use on perovskite solar cells has been challenging due to the richness of the physical processes occurring within similar time domains. The aim of this work is to understand the general impedance response and propose a general equivalent circuit model that accounts for the different processes and give access to quantitative analysis. By systematically modifying the electron selective contacts and the thickness of the perovskite film it has been possible to distinguish between the characteristic impedance signals of the perovskite layer and those arising from the contacts. The study is carried out using mixed organic lead halogen perovskite (FA0.85MA0.15Pb(I0.85Br0.15)3) solar cells with three different electron selective contacts: SnO2, TiO2, and Nb2O5. The contacts have been deposited by atomic layer deposition (ALD), which provides pin-hole free films and excellent thickness control in the absence of a mesoporous layer to simplify the impedance analysis. It was found that the interfacial impedance has a rich structure that reveals different capacitive processes, serial steps for electron extraction, and a prominent inductive loop related to negative capacitance at intermediate frequencies. Overall, the present report provides insights into the impedance response of perovskite solar cells, which enable an understanding on the different electronic/ionic processes taking place during device operation.

To realize the potential of artificial intelligence in medical imaging, improvements in imaging capabilities are required, as well as advances in computing power and algorithms. Hybrid inorganic–organic metal halide perovskites, such as methylammonium lead triiodide (MAPbI₃), offer strong X-ray absorption, high carrier mobilities (µ) and long carrier lifetimes (τ), and they are promising materials for use in X-ray imaging. However, their incorporation into pixelated sensing arrays remains challenging. Here we show that X-ray flat-panel detector arrays based on microcrystalline MAPbI₃ can be created using a two-step manufacturing process. Our approach is based on the mechanical soft sintering of a freestanding absorber layer and the subsequent integration of this layer on a pixelated backplane. Freestanding microcrystalline MAPbI₃ wafers exhibit a sensitivity of 9,300 µC Gy_air^–1 cm^–2 with a μτ product of 4 × 10^–4 cm² V^–1, and the resulting X-ray imaging detector, which has 508 pixels per inch, combines a high spatial resolution of 6 line pairs per millimetre with a low detection limit of 0.22 nGy_air per frame.