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Charge carrier mobility is a fundamental property of semiconductor materials that governs many electronic device characteristics. For metal halide perovskites, a wide range of charge carrier mobilities have been reported using different techniques. Mobilities are often estimated via transient methods assuming an initial charge carrier population after pulsed photoexcitation and measurement of photoconductivity via non-contact or contact techniques. For nanosecond to millisecond transient methods, early-time recombination and exciton-to-free-carrier ratio hinder accurate determination of free-carrier population after photoexcitation. By considering both effects, we estimate long-range charge carrier mobilities over a wide range of photoexcitation densities via transient photoconductivity measurements. We determine long-range mobilities for FA0.83Cs0.17Pb(I0.9Br0.1)3, (FA0.83MA0.17)0.95Cs0.05Pb(I0.9Br0.1)3 and CH3NH3PbI3-xClx polycrystalline films in the range of 0.3 to 6.7 cm2 V−1 s−1. We demonstrate how our data-processing technique can also reveal more precise mobility estimates from non-contact time-resolved microwave conductivity measurements. Importantly, our results indicate that the processing of polycrystalline films significantly affects their long-range mobility. Charge carrier mobility is a fundamental property of semiconductors. The authors of this study demonstrate a novel way to estimate long-range mobilities of perovskite thin-films and single crystals by taking early-time carrier dynamics into account. [ABSTRACT FROM AUTHOR]

While the challenges associated with the stability of metal halide perovskites are well known and intensely studied, variability in electronic properties represents an equally significant, yet seldom studied, challenge that could potentially slow or inhibit the commercial viability of these systems. In this work, the contactless characterization technique time‐resolved microwave conductivity (TRMC) is used to quantify the variability in electronic properties of the prototypical perovskite, methylammonium lead iodide (MAPbI3) both between different samples, and at different locations within the same sample. Using scanning electron microscopy (SEM) and a quasi‐automated image‐analysis strategy, it is possible to evaluate the metrics of heterogeneity in surface microstructure and correlate them with the electronic properties as obtained by TRMC. Substantial intra‐sample and inter‐sample variation is observed in the mobility‐yield product in samples prepared following differing protocols, and in samples prepared following identical protocols. [ABSTRACT FROM AUTHOR]

Designed to outperform conventional computers when performing machine-learning tasks, neuromorphic computation is the principle whereby certain aspects of the human brain are replicated in hardware. While great progress has been made in this field in recent years, almost all input signals provided to neuromorphic processors are still designed for traditional (von Neumann) computer architectures. Here, we show that a simple photosensitive capacitor will inherently reproduce certain aspects of biological retinas. We found that capacitors based on metal halide perovskites will output a brief voltage spike in response to changes in incident light intensity, but output zero voltage under constant illumination. Such a sensor is not only optimized for use with spiking neuromorphic processors but also anticipated to have broad appeal from fields such as light detection and ranging, autonomous vehicles, facile recognition, navigation, and robotics. [ABSTRACT FROM AUTHOR]

The light-soaking effect is the observation that under constant illumination the measured power conversion efficiency of certain solar cells changes as a function of time. The theory of the light-soaking in metal halide perovskites is at present incomplete. In this report, we employ steady-state microwave conductivity, a contactless probe of electronic properties of semiconductors, to study the light-soaking effect in metal halide perovskites. By illuminating isolated thin films of two mixed-cation perovskites with AM1.5 solar illumination, we observe a continual increase in photoconductance over a period of many (>12) hours. We can fit the experimentally observed changes in photoconductance to a stretched exponential function, in an analogous manner to bias-stressed thin-film transistors. The information provided in this report should help the community better understand one of the most perplexing open problems in the field of perovskite solar cells and, ultimately, lead to more robust and predictable devices. The light soaking effect is when the power conversion efficiency of a solar cell changes over time while the illumination remains constant. Here, the authors investigate the underlying mechanisms of the light soaking effect in metal halide perovskites using steady-state microwave conductivity. Under constant illumination they observe an increase in photoconductance over many hours. [ABSTRACT FROM AUTHOR]