Perovskite materials - Page 12

Researchers at UNIST, POSTECH and the University of Pennsylvania have created a new perovskite-based nanocatalyst that can be used to recycle major greenhouse gases, such as methane (CH₄) and carbon dioxide (CO₂), into valuable hydrogen (H₂) gas.

The new catalyst is hoped to promote various waste-to-energy conversion technologies, as it has over twice the conversion efficiency from CH₄ to H₂ than the traditional electrode catalysts.

Scientists at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) have developed a new wide-bandgap perovskite layer – called Apex Flex – which they claim is able to withstand heat, light, and operational tests, and at the same time provide a reliable and high voltage.

With this material, they have built tandem solar cells with 23.1% power conversion efficiency on a rigid substrate, and 21.3% on flexible plastic. The new Apex Flex wide-bandgap perovskite recombination layer is grown with atomic layer deposition (ALD). The new material is described as a “nucleation layer consisting of an ultra-thin polymer with nucleophilic hydroxyl and amine functional groups for nucleating a conformal, low-conductivity aluminum zinc oxide layer.”

Scientists at UC San Diego have developed a new method to fabricate perovskites as single-crystal thin films, which are more efficient for use in solar cells and optical devices than the current state-of-the-art polycrystalline forms of the material.

Their fabrication method - which uses standard semiconductor fabrication processes - results in flexible single-crystal perovskite films with controlled area, thickness, and composition. These single-crystal films showed fewer defects, greater efficiency, and enhanced stability than their polycrystalline counterparts, which could lead to the use of perovskites in solar cells, LEDs, and photodetectors.

Osman M. Bakr's group in the KAUST Catalysis Facility has designed a low-temperature method that can be useful for making improved single crystal perovskites. The team said that novel perovskites have positive and negative ions in the same plan as the natural perovskite calcium titanate (CaTiO₃). Lead halide perovskites, having lead ions as well as halide ions, such as chlorine and iodine in the perovskite mix, are drawing attention for optoelectronic applications.

The crystals have previously been created using high temperatures, however these have created many challenges. Now, the KAUST team has developed a new approach, enabling better crystals to form.

A research group led by Prof. Luo Junhua from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences reported the first halide double perovskite ferroelectric, (n-propylammonium)₂CsAgBiBr₇, which exhibits distinct ferroelectricity with a notable saturation polarization of about 1.5 μCcm^-2.

Halide double perovskites have been found to be a promising environmentally friendly optoelectronic and photovoltaic material, exhibiting inherent thermodynamic stability, high defect tolerance and appropriate band gaps. However, no ferroelectric material based on halide double perovskites has been discovered until now.

An international team of scientists recently developed a new composite material based on perovskite nanocrystals to fabricate miniature light sources with improved performance.

Protection of perovskite nanocrystals within porous glass microspheres made it possible to increase their stability by almost 3 times. Moreover, the subsequent coating of these particles with polymers resulted in the fabrication of water-dispersible luminescent microspheres based on CsPbBr₃ nanocrystals. This method of fabrication is especially important for the implementation of perovskite nanocrystals in diverse biological applications.

Scientists have theorized that organometallic halide perovskites are so promising due to a highly controversial mechanism called the Rashba effect. Scientists at the U.S. Department of Energy's Ames Laboratory have now experimentally proven the existence of the effect in bulk perovskites, using short microwave bursts of light to both produce and then record a rhythm, much like music, of the quantum coupled motion of atoms and electrons in these materials.

Research thus far hypothesized that the materials' extraordinary electronic, magnetic and optical properties are related to the Rashba effect, a mechanism that controls the magnetic and electronic structure and charge carrier lifetimes. But despite intense study and debate, conclusive evidence of Rashba effects in bulk organometallic halide perovskites, used in the most efficient perovskite solar cells, remained highly elusive.

University of Groningen scientists are investigating in situ how lead-free perovskite crystals form and how the crystal structure affects the functioning of the solar cells, as part of their quest to find alternatives to lead-based perovskites.

The best results in solar cells have been obtained using perovskites with lead as the central cation. As this metal is toxic, tin-based alternatives have been developed, for example, formamidinium tin iodide (FASnI₃). This is a promising material; however, it lacks the stability of some of the lead-based materials. Attempts have been made to mix the 3D FASnI₃ crystals with layered materials, containing the organic cation phenylethylammonium (PEA). "My colleague, Professor Maria Loi, and her research team showed that adding a small amount of this PEA produces a more stable and efficient material," says Assistant Professor Giuseppe Portale.

Researchers at the Weizmann Institute of Science have found that in halide perovskites, creating defects takes more effort than restoring order. This finding may explain the remarkable properties of halide perovskites and help develop a new approach to controlling the properties of these and other materials.

Much about Halide perovskites still puzzles researchers; in particular, it has been unclear why they can contain relatively few defects, on the order of 1010 per cubic centimeter (that is, one defect for every trillion atoms, instead of the one to a hundred for every million, as in regular semiconductors). This concentration of defects rivals that of germanium crystals, among the cleanest solid-state man-made materials. Getting close to such a low defect concentration in the semiconductors used in today's electronic devices requires enormous effort and ingenuity. In contrast, halide perovskites can be produced within a fraction of a second by mixing simple chemical salt solutions at near room temperature.

Researchers at the University of California, Irvine and other institutions have developed a new process for producing oxide perovskite crystals in flexible, free-standing layers.

'Through our successful fabrication of ultrathin perovskite oxides down to the monolayer limit, we've created a new class of two-dimensional materials,' said co-author Xiaoqing Pan, professor of materials science & engineering at UCI. 'Since these crystals have strongly correlated effects, we anticipate they will exhibit qualities similar to graphene that will be foundational to next-generation energy and information technologies.'