With rapid progress in the deployment of metal halide perovskites in various device applications such as solar cells, light-emitting devices, field-effect transistors, photodetectors, etc., the next eminent focus is on the single crystals of these materials. With a lack of grain boundaries and low trap densities, remarkably long charge carrier diffusion lengths, and high ambient and operational stabilities, this class of materials seems greatly promising. Yet, the growing concern for lead toxicity in commercial semiconductor devices has entailed a thrust in the research of alternative lead-free perovskites, including their single crystalline forms. However, there is still no consolidated account of the state-of-the-art in this domain and accordingly, countless feasible systems still remain unexplored. To bridge this gap, we attempt to provide here, an up-to-date overview of lead-free perovskite single crystals with respect to their synthesis methods, structural diversity, stability, photophysical and electrical properties, and device applications. We discuss various approaches to designing, modeling, fabricating, and characterizing new single-crystal systems and conclude with some critical insights for further investigating this field of research.

CsPbBr 3 single crystals have potential for application in ionizing-radiation detection devices due to their optimal optoelectronic properties. Yet, their mixed ionic–electronic conductivity produces instability and hysteretic artifacts hindering the long-term device operation. Herein, we report an electrical characterization of CsPbBr 3 single crystals operating up to the time scale of hours. Our fast time-of-flight measurements reveal bulk mobilities of 13–26 cm 2 V –1 s –1 with a negative voltage bias dependency. By means of a guard ring (GR) configuration, we separate bulk and surface mobilities showing significant qualitative and quantitative transport differences. Our experiments of current transients and impedance spectroscopy indicate the formation of several regimes of space-charge-limited current (SCLC) associated with mechanisms similar to the Poole–Frenkel ionized-trap-assisted transport. We show that the ionic-SCLC seems to be an operational mode in this lead halide perovskite, despite the fact that experiments can be designed where the contribution of mobile ions to transport is negligible.

Self-healing of defects imposed by external stimuli such as high energy radiation is a possibility to sustain the operational lifetime of electronic devices such as radiation detectors. Cs 3 Bi 2 Br 3 I 6 polycrystalline wafers are introduced here as novel X-ray detector material, which not only guarantees a high X-ray stopping power due to its composition with elements with high atomic numbers, but also outperforms other Bi-based semiconductors in respect to detector parameters such as detection limit, transient behavior, or dark current. The polycrystalline wafers represent a size scalable technology suitable for future integration in imager devices for medical applications. Most astonishingly, aging of these wafer-based devices results in an overall improvement of the detector performance-dark currents are reduced, photocurrents are increased, and one of the most problematic properties of X-ray detectors, the base line drift is reduced by orders of magnitude. These aging induced improvements indicate self-healing effects which are shown to result from recrystallization. Optimized synthetic conditions also improve the as prepared X-ray detectors; however, the aged device outperforms all others. Thus, self-healing acts in Cs 3 Bi 2 Br 3 I 6 as an optimization tool, which is certainly not restricted to this single compound, it is expected to be beneficial also for many further polycrystalline ionic semiconductors.

diodes, [3] electromagnetic shielding, [4] and organic photovoltaics. [5] Electrodes based on metallic nanowires (NWs) are among the most promising alternatives to indium tin oxide (ITO), which is currently the most efficient and widely used transparent conducting material. [6] Silver, the metal with the highest electrical conductivity, can be expected to provide the best network electrodes. [7] Indeed, silver nanowires (Ag NWs)-based percolating networks successfully combine high flexibility, high optical transparency, and high electrical conductivity. [8] Ag NWs electrode are also cost-efficient and compatible with large-scale manufacturing methods. [5a] However, they are very vulnerable to heat, light, oxygen, humidity, and sulfidation, limiting their usefulness for practical applications. [9] Solutions to these problems have been investigated and various methods were applied to protect the Ag NWs. [10] Recently, a SnO x shell was proposed as a solution to overcome the stability issues. [11] Zhao et al. reported the wet chemical synthesis of Ag NWs with a monolayer of SnO 2 under ambient conditions. [11a] This is achieved by introducing trace amounts of Sn 2+ to an Ag NWs dispersion, which form an oxide monolayer. This Transparent electrodes consisting of silver nanowires (Ag NWs) are a solution-processed alternative to commonly used indium tin oxide electrodes. Here, Ag NW electrodes protected by a tin oxide (SnO x ) are explored and unprecedented thermal stability is found. While unprotected Ag NW electrodes fail at 250 °C, the SnO x Ag NW electrodes remain stable for 40 h at 250 °C and withstand high temperatures up to 500 °C for short times. First, an optimized method of synthesis that provides uniform Ag NWs with high reproducibility is used. Afterward, a SnO x shell is formed in a wet chemical reaction. Fabrication of highly conductive electrodes requires thermal annealing at 300 °C for 5 min under ambient atmosphere. Electrodes with a sheet resistance as low as 20 Ω sq -1 and visible transmittance of 84% are demonstrated. It is shown that a ≈2 nm thick SnO x shell effectively protects the Ag NWs in a temperature range between 200 and 500 °C, whereas unprotected Ag NWs suddenly fail at temperatures beyond 200 °C. It is strongly anticipated that these improvements in the stability of Ag NWs open a large field of further investigations and applications.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/aelm.202100787.

Aerosol deposition (AD) is a promising additive manufacturing method to fabricate low‐cost, scalable films at room temperature, but has not been considered for semiconductor processing, so far. The successful preparation of cesium lead tribromide (CsPbBr3) perovskite films on interdigitated indium tin oxide (ITO) electrodes by means of AD is reported here. The 20–35 µm thick layers are dense and have good adhesion to the substrate. The orthorhombic Pnma crystal structure of the precursor powder was retained during the deposition process with no signs of defect formation. The formation of electronic defects by photoluminescence spectroscopy is investigated and found slightly increased carrier recombination from defect sites for AD films compared to the powder. A nonuniform defect distribution across the layer, presumably induced by the impact of the semiconducting grains on the hard substrate surface, is revealed. The opto‐electronic properties of AD processed semiconducting films is further tested by electrical measurements and confirmed good semiconducting properties and high responsivity for the films. These results demonstrate that AD processing of metal halide perovskites is possible for opto‐electronic device manufacturing on 3D surfaces. It is believed that this work paves the way for the fabrication of previously unimaginable opto‐electronic devices by additive manufacturing.