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The hole‐transporting material (HTM) in perovskite solar cells (PSCs) provides an ideal interface with the perovskite layer for hole collection while influencing the perovskite crystalline structure and morphology. This article presents SIM and DIM, two new dopant‐free imidazolium‐based HTMs with charged units accompanied by counter ions that show the potential to function as ionic HTMs and ionic liquid additives and help improve the efficiency and stability of inverted PSCs. DIM‐based PSCs demonstrates exceptional performance with a high‐power conversion efficiency of 19.15%, attributed to improved passivation of perovskite interface defects. Furthermore, these new imidazolium salt‐based HTMs can be manufactured economically, making them a viable option for mass production and PSC commercialization. [ABSTRACT FROM AUTHOR]

In the operating mechanisms of perovskite solar cells, hole-transporting materials (HTMs) facilitate directional charge transfer and electron blocking. In addition, HTMs are also important in forming the perovskite layers for inverted perovskite solar cells, improving device efficiency. We present a method for increasing efficiency by ionizing HTMs, introducing defect-passivating abilities, improved interfacial properties, and ideal surface topographies. Compared to their non-ionized counterpart, the ionic HTMs have well-matched energy levels and smooth perovskite layers, resulting in higher short-circuit current densities. These experimental findings are corroborated by atomistic first principle electronic structure calculations of model perovskite systems. Furthermore, we conducted a comparative study of different ionizing counter anions for HTMs. The iodide-based ionic HTM, PMO-I, has a maximum efficiency of 20.46%, 1.71% higher than that of the non-ionic HTM, PMO (18.75%). [ABSTRACT FROM AUTHOR]

The perovskite polycrystalline thin film detector fabricated by solution method is a promising low‐cost, scalable technology for radiation imaging, but its thin volume limits the sensing efficiency for high‐energy X‐ray photons. This work reports 2D perovskite thin film photo‐diodes with a detection gain when sensing visible and X‐ray photons. Detailed power and temperature‐dependent device characterizations reveal a charge multiplication effect to be responsible for the observed high gain. This is caused by a disparity in electron and hole transport, where electron transport is retarded by a trap/de‐trap process via shallow trap states, whereas the hole transport is fast enough to produce a photoconductive gain in satisfying the charge neutrality. The 2D perovskite made with butylamine spacers is also found to exhibit a larger efficiency gain than those made with phenylethylamines because of the higher likelihood of forming shallow traps in the former. The thin film diodes feature a high temporal response over 1 MHz due to the fast charge collection across a thin volume, and the discovery provides device physics mechanisms in connection to material structure‐function relationship for future optoelectronics design that can boost the efficiency of X‐ray sensing and dim light detection. [ABSTRACT FROM AUTHOR]

Hydrovoltaic technology is a promising approach for clean and renewable energy generation, owing to its unique ability to generate electricity from the interactions between nanomaterials and abundant water. However, the output current of hydroelectric generators, which is usually below 1 mA, needs improvement. Here, we demonstrate a large-scale integration of water-graphite hydroelectric generators that can produce an output current of up to 58 mA, surpassing the performance of existing hydroelectric generators, and capable of powering commercial electronics, such as electric fans and full-color liquid crystal display screens. Our results show that this low-cost and scalable hydroelectric generator has the potential to significantly expand the application domain and facilitate the development of clean and renewable energy sources. [ABSTRACT FROM AUTHOR]

Perovskite photovoltaics (PVs) are an emerging solar energy generation technology that is nearing commercialization. Despite the unprecedented progress in increasing power conversion efficiency (PCE) for perovskite solar cells (PSCs), up‐scaling lab‐made cells to solar modules remains a challenge. In this work, the recent progress of making perovskite mini‐modules is reviewed. In particular, a database summarizing the module size, performance, hysteresis, and operational lifetimes reported in the literature is built. After analyzing the performance losses from scaling PSCs to mini‐modules based on the data collected from the literature, the current key to high‐performance perovskite mini‐modules is found to be the coating method optimization. If the perovskite layer quality is well reserved, a >24% mini‐module efficiency is projected by only considering the losses from lateral resistivity and laser scribing area. Next, performance characteristics are explored including hysteresis and meta‐stable power outputs that must be overcome to correctly characterize perovskite modules. Finally, current challenges associated with the long‐term stability of perovskite modules are examined and the importance of such durability for commercialization is discussed. It is hoped that the findings in this review provide a bridge for the development of perovskite modules that will lead to commercialization in the near future. [ABSTRACT FROM AUTHOR]

Interfacing chiral molecules with achiral semiconductor nanomaterials has been shown to induce chiroptical (i.e., preferential absorption of circularly polarized light) signatures. This chirality transfer phenomena is attractive for enhancing the functionality of nanomaterials by making them sensitive to the circular polarization states of photons, and attractive for selective optical sensing applications. Chirality transfer via interfacing chiral molecules with nanomaterial surfaces generally gives small sensitivities as determined by anisotropy factors, the ratio of polarized and linear absorption. Here we use atomistic time-dependent density functional theory simulations to investigate the molecular properties which influence the chiroptical signatures of a lead-halide perovskite cluster. First, we find that for chiral molecules that contain aryl groups, such as (R/S)-methylbenzylamine and (R/S)-methylphenyl acetic acid, modulating their molecular dipole via meso functionalization with strong withdrawing groups, such as NO2, can enhance intensities of chiroptical signatures. Second, using the lactic acid series ((S)-lactic, (S)-malic, and (S,S) tartaric acid) we average over conformations of these molecules on the cluster surface. We find that limited conformational flexibility of lactic acid provides the largest chiroptical intensities while signal from tartaric acid quenches after conformational average. These results demonstrate an importance of chemical functionalization leading to a polarized chiral system. Altogether, either through acid–base equilibrium or strategic functionalization, and limited conformationally degrees of freedom are important for obtaining high-intensity nanomaterial chiroptical signatures through chirality transfer. [ABSTRACT FROM AUTHOR]

Interface‐type (IT) metal/oxide Schottky memristive devices have attracted considerable attention over filament‐type (FT) devices for neuromorphic computing because of their uniform, filament‐free, and analog resistive switching (RS) characteristics. The most recent IT devices are based on oxygen ions and vacancies movement to alter interfacial Schottky barrier parameters and thereby control RS properties. However, the reliability and stability of these devices have been significantly affected by the undesired diffusion of ionic species. Herein, a reliable interface‐dominated memristive device is demonstrated using a simple Au/Nb‐doped SrTiO3 (Nb:STO) Schottky structure. The Au/Nb:STO Schottky barrier modulation by charge trapping and detrapping is responsible for the analog resistive switching characteristics. Because of its interface‐controlled RS, the proposed device shows low device‐to‐device, cell‐to‐cell, and cycle‐to‐cycle variability while maintaining high repeatability and stability during endurance and retention tests. Furthermore, the Au/Nb:STO IT memristive device exhibits versatile synaptic functions with an excellent uniformity, programmability, and reliability. A simulated artificial neural network with Au/Nb:STO synapses achieves a high recognition accuracy of 94.72% for large digit recognition from MNIST database. These results suggest that IT resistive switching can be potentially used for artificial synapses to build next‐generation neuromorphic computing. [ABSTRACT FROM AUTHOR]

The prototypical chalcogenide perovskite, BaZrS3 (BZS), with its direct bandgap of 1.7–1.8 eV, high chemical stability, and strong light–matter interactions, has garnered significant interest over the past few years. So far, attempts to grow BaZrS3 films have been limited mainly to physical vapor deposition techniques. Here, we report the fabrication of BZS thin films via a facile aqueous solution route of polymer-assisted deposition (PAD), where the polymer-chelated cation precursor films were sulfurized in a mixed CS2 and Ar atmosphere. The formation of a single-phase polycrystalline BZS thin film at a processing temperature of 900 °C was confirmed by X-ray diffraction and Raman spectroscopy. The stoichiometry of the films was verified by Rutherford Backscattering spectrometry and energy-dispersive X-ray spectroscopy. The BZS films showed a photoluminescence peak at around 1.8 eV and exhibited a photogenerated current under light illumination at a wavelength of 530 nm. Temperature-dependent resistivity analysis revealed that the conduction of BaZrS3 films under the dark condition could be described by the Efros–Shklovskii variable range hopping model in the temperature range of 60–300 K, with an activation energy of about 44 meV. [ABSTRACT FROM AUTHOR]

Metal-halide perovskites are emerging materials for radiation sensing featuring high absorption cross section, high charge mobility, and long carrier lifetime enabling superior detection efficiencies even at room temperature. Perovskite detector technologies are more complex involving different detecting modes and device architectures. To elucidate the working principles, we provide a Perspective on the device structures and the operational principles of halide perovskite direct conversion detectors for radiation sensing. We will first discuss different detection modes and introduce the commonly used device architectures and their working principles. Based on our work and pioneer developments in the field, we will next compare the performances of the reported detectors. Additionally, we will summarize the single crystal detectors and polycrystalline thin film devices and discuss their advantages and disadvantages for different applications. Finally, we provide a future Perspective on the critical problems that must be addressed to commercialize this technology. [ABSTRACT FROM AUTHOR]

Interface‐type (IT) resistive switching (RS) memories are promising for next generation memory and computing technologies owing to the filament‐free switching, high on/off ratio, low power consumption, and low spatial variability. Although the switching mechanisms of memristors have been widely studied in filament‐type devices, they are largely unknown in IT memristors. In this work, using the simple Au/Nb:SrTiO3 (Nb:STO) as a model Schottky system, it is identified that protons from moisture are key element in determining the RS characteristics in IT memristors. The Au/Nb:STO devices show typical Schottky interface controlled current–voltage (I–V) curves with a large on/off ratio under ambient conditions. Surprisingly, in a controlled environment without protons/moisture, the large I–V hysteresis collapses with the disappearance of a high resistance state (HRS) and the Schottky barrier. Once the devices are re‐exposed to a humid environment, the typical large I–V hysteresis can be recovered within hours as the HRS and Schottky interface are restored. The RS mechanism in Au/Nb:STO is attributed to the Schottky barrier modulation by a proton assisted electron trapping and detrapping process. This work highlights the important role of protons/moisture in the RS properties of IT memristors and provides fundamental insight for switching mechanisms in metal oxides‐based memory devices. [ABSTRACT FROM AUTHOR]

Magnetoelectric coupling is achieved near room temperature in a spin crossover FeII molecule‐based compound, [Fe(1bpp)2](BF4)2. Large atomic displacements resulting from Jahn–Teller distortions induce a change in the molecule dipole moment when switching between high‐spin and low‐spin states leading to a step‐wise change in the electric polarization and dielectric constant. For temperatures in the region of bistability, the changes in magnetic and electrical properties are induced with a remarkably low magnetic field of 3 T. This result represents a successful expansion of magnetoelectric spin crossovers towards ambient conditions. Moreover, the observed 0.3–0.4 mC m−2 changes in the H‐induced electric polarization suggest that the high strength of the coupling obtained via this route is accessible not just at cryogenic temperatures but also near room temperature, a feature that is especially appealing in the light of practical applications. [ABSTRACT FROM AUTHOR]

Metal halide perovskite nanocrystals are recent emerging light emitters with high emission quantum yields and wide color tunability from the ultraviolet to near infrared regions. Perovskite nanocrystals have been applied in high-performance optoelectronics such as bright light-emitting diodes, high-resolution X-ray imaging and photo/radiation sensors, and have received wide attention in this field. However, key challenges such as the poor material stability in the ambient environment and the short operational lifetime under external stress such as an electrical field or illumination still hinder the further development of perovskite nanocrystal-based optoelectronics. Recent intriguing works have smartly incorporated perovskite nanocrystals in metal–organic framework (MOF) matrices to stabilize their emission properties. The resulting perovskite–MOF structures are bright light emitters that have enabled a variety of promising applications. This perspective provides an overview of the recent progress in perovskite/MOF heterostructures and their applications in photonic devices. It first introduces the challenges of stabilizing perovskite nanocrystals, and then discusses how perovskite/MOF structures overcome these problems. We then go over the development of photonic devices using perovskite/MOF as light emitters and describe their potential uses in clean energy conversion and sensing applications. [ABSTRACT FROM AUTHOR]

Interfaces play a decisive role in perovskite solar cells' power conversion efficiency and their long‐term durability. Small‐molecule hole‐transporting materials (HTMs) have grabbed enormous attention due to their structural flexibility, material properties, and stabilities, allowing for improved operational durability in perovskite photovoltaics. This study synthesizes and investigates a new class of benzimidazole‐based small molecules, named YJS001 and YJS003, serving as the HTMs to enable high‐efficiency mixed‐cation mixed‐halide perovskite solar cells. The benzimidazole‐based materials are dopant‐free HTMs composed of donor and acceptor building blocks that are designed to engineer the energy level alignment near the HTM/perovskite interface. Mixed‐cation mixed‐halide perovskites can be grown uniformly on both HTMs with large crystalline grains. It is discovered that the donor‐rich YJS003‐based solar cell exhibits a high open‐circuit voltage of 1.09 V with a champion power conversion efficiency of over 20%. Power‐dependent current–voltage characteristics of the solar cells are analyzed, from which the high performance of YJS003's excellent hole mobility and well‐aligned energy level is attributed. This work introduces a new class of benzimidazole‐based small molecules as HTMs, that paves the path for dopant free interface material development for commercialization of perovskite solar cells. [ABSTRACT FROM AUTHOR]

Metal halide perovskites are not only established as champion materials for conversion of solar energy to electricity but are also one of the promising candidates for solar driven fuel generation. In this paper, we report the photovoltaic devices' operational stability investigation in dry and humid nitrogen (N2) and carbon dioxide (CO2) environments. By monitoring the behavior of a mixed-cation mixed-halide perovskite solar cell under constant 1-sun illumination in a gas mixture, we find that relative humidity plays a central role in expediting degradation. Interestingly, rapid degradation is a recoverable process once the light source is removed at the same humidity level. After a detailed analysis of the current–voltage characteristics, an increase in the series resistance is observed when exposed to continuous illumination. This is validated by surface resistivity measurements on both sides of the device. Photoluminescence (PL) characterization indicates a temporary decrease in the PL intensity and can be expedited by higher relative humidity levels. Our study reports behavior of perovskite solar cells in dry and wet N2 and CO2 environments that is necessary for solar-to-fuel applications like CO2 reduction and water splitting in the gas phase. [ABSTRACT FROM AUTHOR]

Mixed A-cation halide perovskites have emerged as one of the most promising materials for next-generation optoelectronic applications due to such factors as attractive charge carrier transport properties and enhanced stability under operating conditions. However, the influence of A-cation mixing on the excited state charge carrier dynamics and, particularly, on ultrafast hot-carrier relaxation processes, is yet to be studied in sufficient detail. We combine nonadiabatic molecular dynamics and time-domain density functional theory methods to establish the impact of formamidinium (FA)–cesium (Cs) mixing on the subpicosecond-scale hot-charge carrier cooling processes in FA1−xCsxPbI3 (x ≤ 0.5) materials. Our ab initio study illustrates that the partial substitution of organic FA species with inorganic Cs cations substantially extends the hot-electron and hot-hole relaxation times. Observed increases in the hot-carrier lifetimes indicate better performance of FA1−xCsxPbI3 compared to parent FAPbI3 in the field of hot carrier solar cells. The atomistic details of lattice dynamics reveal that FA–Cs cation mixing partially suppresses thermal fluctuations in the structure, weakening the carrier–phonon interaction under ambient conditions. Increased structural rigidity and weakened carrier–phonon interactions in turn lower the rates of intraband nonadiabatic transitions of hot-carriers and enhance their excited state lifetimes. The in-depth understanding of the relationship between the dynamic structure and carrier relaxation allows us to further propose rational design principles that can enhance the hot-carrier lifetimes in photoactive materials. The computational guides will help to realize photovoltaic devices that efficiently harvest hot-carriers and exhibit an improved power conversion performance compared to traditional single-junction solar cells. [ABSTRACT FROM AUTHOR]