Search

Double perovskite halides are a class of materials with diverse chemistries that are amenable to solution-based synthesis routes, and display a range of properties for a variety of potential applications. Starting from a consideration of the octahedral and tolerance factors of ∼2000 candidate double perovskite compounds, we compute structural, electronic, and transport properties of ∼1000 using first-principles calculations based on density-functional-theory methods. The computational results have been assembled in a database that is accessible through the Materials Project online. As one potential application, double perovskites are candidates in the search for lead-free halide photovoltaic absorbers. We present the application of our database to aid the discovery of new double perovskite halide photovoltaic materials, by combining the results with optical absorption and phonon stability calculations. From three distinct classes of chemistries, 11 compounds were identified as promising solar absorbers and the complex chemical trends for band gap within each of these are analyzed, to provide guidelines for the use of substitutional alloying as a means of further tuning the electronic structure. Other possible applications of the database are also discussed.

Si photocathodes integrated with Ag-supported dendritic Cu catalysts are used to perform light-driven reduction of CO2 to C2 and C3 products in aqueous solution. A back illumination geometry with an n-type Si absorber was used to permit the use of absorbing metallic catalysts. Selective carrier collection was accomplished by a p+ implantation on the illumination side and an n+ implantation followed by atomic layer deposition of TiO2 on the electrolyte site. The Ag-supported dendritic Cu CO2 reduction catalyst was formed by evaporation of Ag followed by high-rate electrodeposition of Cu to form a high surface area structure. Under simulated 1 sun illumination in 0.1 M CsHCO3 saturated with CO2, the photovoltage generated by the Si (∼600 mV) enables C2 and C3 products to be produced at -0.4 vs. RHE. Texturing of both sides of the Si increases the light-limited current density, due to reduced reflection on the illumination side, and also deceases the onset potential. Under simulated diurnal illumination conditions photocathodes maintain over 60% faradaic efficiency to hydrocarbon and oxygenate products (mainly ethylene, ethanol, propanol) for several days. After 10 days of testing, contamination from the counter electrode is observed, which causes an increase in hydrogen production. This effect is mitigated by a regeneration procedure which restores the original catalyst selectivity. A tandem, self-powered CO2 reduction device was formed by coupling a Si photocathode with two series-connected semitransparent CH3NH3PbI3 perovskite solar cells, achieving an efficiency for the conversion of sunlight to hydrocarbons and oxygenates of 1.5% (3.5% for all products).

The human nervous system inspires the next generation of sensory and communication systems for robotics, human‐machine interfaces (HMIs), biomedical applications, and artificial intelligence. Neuromorphic approaches address processing challenges; however, the vast number of sensors and their large‐scale distribution complicate analog data manipulation. Conventional digital multiplexers are limited by complex circuit architecture and high supply voltage. Large sensory arrays further complicate wiring. An ʻin‐electrolyte computingʼ platform is presented by integrating organic electrochemical transistors (OECTs) with a solid‐state polymer electrolyte. These devices use synapse‐like signal transport and spatially dependent bulk ionic doping, achieving over 400 times modulation in channel conductance, allowing discrimination of locally random‐access events without peripheral circuitry or address assignment. It demonstrates information processing from 12 tactile sensors with a single OECT output, showing clear advantages in circuit simplicity over existing all‐electronic, all‐digital implementations. This self‐multiplexer platform offers exciting prospects for circuit‐free integration with sensory arrays for high‐quality, large‐volume analog signal processing. [ABSTRACT FROM AUTHOR]

The use of sunlight to drive organic reactions constitutes a green and sustainable strategy for organic synthesis. Herein, we discovered that the earth-abundant aluminum oxide (Al2O3) though paradigmatically known to be an insulator could induce an immense increase in the selective photo-oxidation of different benzyl alcohols in the presence of a large variety of dyes and O2. This unique phenomenon is based on the surface complexation of benzyl alcohol (BnOH) with the Brønsted base sites on Al2O3, which reduces its oxidation potential and causes an upshift in its HOMO for electron abstraction by the dye. The surface complexation of O2 with Al2O3 also activates the adsorbed O2 for receiving electrons from the photoexcited dyes. This discovery brings forth a new understanding on utilizing surface complexation mechanisms between the reactants and earth abundant materials to effectively achieve a wider range of photoredox reactions.

Owing to their synthetic versatility and optoelectronic tunability, low-dimensional hybrid metal halide perovskites (MHPs) provide a key avenue for the design of future optoelectronic materials. Nuclear magnetic resonance (NMR) spectroscopy has emerged as a powerful tool for structural characterisation and molecular dynamics elucidation in MHPs, which are known to control the materials' optoelectronic properties. In this work, we utilise solid state NMR to study structurally diverse hybrid MHPs containing 2D, 1D and 0D inorganic motifs that are templated by a series of xylylenediammonium cations and compare their characteristics with those of archetype 3D perovskites. The highly resolved scalar coupling pattern (J¹(207Pb–79/81Br) = 1.98 kHz) in the 207Pb NMR spectrum of 0D meta-xylylenediammonium lead bromide ((mXDA)2PbBr6), reveals that 207Pb NMR of methylammonium lead bromide (MAPbBr3) and formadinium lead bromide (FAPbBr3) is sensitive to local Br positional disorder, associated with the fast reorientation of the MA/FA cations. Variable temperature ¹H spin–lattice relaxation quantifies the correlation time of the reorientation of the MA/FA cations at picosecond timescales, in contrast to the slower motion of the bulky cations in the low-dimensional perovskites. Additionally, the study of meta-xylylenediammonium tin halides ((mXDA)2SnX6) provides the first direct detection of tin-halide scalar coupling patterns (J¹(119Sn–79/81Br) = 1.51 kHz; J¹(119Sn–35/37Cl) = 260 Hz). [ABSTRACT FROM AUTHOR]

Lead halide perovskites have revolutionized the field of optoelectronics (such as photovoltaics and light emitting diodes) demonstrating extraordinary material properties despite being formed at low temperatures. However, ion migration in the bulk or at the interfaces results in stability issues especially in devices where metal electrodes directly interface with the perovskite film. Utilizing the switchable photovoltaic phenomenon (SPV) in halide perovskites as a measure of ion migration and electrochemical reactions within them, Cs0.05MA0.15FA0.70PbI2.5Br0.5 triple cation perovskite, widely used in photovoltaics is evaluated. The various factors determining the SPV, including electric field magnitudes, type of metal contacts, Illumination conditions, and temperature is systematically measured. This study reveals the roles of electrode work functions and reactivities on ion migration and local electronic structure modulation. ITO electrodes demonstrated the highest open‐circuit voltage (Voc) about 0.85 V while Ag electrodes developed conductive filaments. However, the Voc distribution for Ti and Cr electrodes shows a more pronounced linear correlation with the poling electric field strength. Insights from this lateral design are directly relevant to transistor and memristor architectures and offer inputs into the design of perovskite‐based photovoltaic/optoelectronic devices. [ABSTRACT FROM AUTHOR]