Methylammonium lead tribromide (CH3NH3PbBr3) single crystals has gained a growing attention in the past few years due to their use as model material to investigate relevant intrinsic perovskite properties, and for their potential applications for radiation detection. Their study has been facilitated by the ease and speed of fabrication of millimetric single crystals through a simple protocol of unseeded Inverse Temperature Crystallization (ITC). In this study, we show that such growing conditions suffer from both insufficient reproducibility regarding crystal quality and

encountered in solar cell engineering. One of them is caused by the presence of mobile ions and how these species alter the internal electrical field, interact with the contact materials, or modulate electronic properties. [3-6] Upon biasing, charged moving ions accumulate in the vicinity of the outer interfaces causing electrical field partial shielding. [7-9] It has also been reported how intrinsic defects chemically react with the electrodes giving rise to losses in performance and device instabilities. [10,11] The occurrence of polarized interfaces in hybrid perovskite-based electronic devices was proposed [12] as an explaining mechanism for the measured excess capacitance at low frequencies. In dark conditions, mobile ions pile up at outer interfaces forming double layer-like structures in the vicinity of the perovskite/contact interface. [13,14] Excess dark capacitance of order 1-10 μF cm −2 can be readily explained in this way. In addition to purely electrostatic approaches for the interfacial phenomena, it is known that chemical reactions between mobile ions and contacting materials might give rise to the formation of dipole-like structures. [15,16] Also, deviations from stable electrical characteristics (i.e., hysteresis in current density-voltage J-V or non-ohmic response) have previously been correlated with the dynamics of migrating ions that interact with the contacts. [14,15,17] A survey about the chemical reactivity of the perovskite/contact materials can be found elsewhere. [14] In this sense, the kinetics of electrode charging may be understood not only Metal halide perovskite single crystals are being explored as functional materials for a variety of optoelectronic applications. Among others, solar cells, field-effect transistors, and X-and γ-ray detectors have shown improved performance and stability. However, a general uncertainty exists about the relevant mechanisms governing the electronic operation. This is caused by the presence of mobile ions and how these defect species alter the internal electrical field, interact with the contact materials, or modulate electronic properties. Here, a set of high-quality thick methylammonium lead tribromide single crystals contacted with low-reactivity chromium electrodes are analyzed by impedance spectroscopy. Through examination of the sample resistance evolution with bias and releasing time, it is revealed that an interplay exists between the perovskite electronic conductivity and the defect distribution within the crystal bulk. Ion diffusion after bias removing changes the local doping density then governing the electronic transport. These findings indicate that the coupling between ionic and electronic properties relies upon a dynamic doping effect caused by moving ions that act as mobile dopants. In addition to electronic features, the analysis extracts values for the ion diffusivity in the range of 10 −8 cm 2 s −1 in good agreement with other independent measurements.

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