Technical / research - Page 27

Researchers from Duke University, Purdue University,  Yale University, Lawrence Berkeley National Laboratory, Chinese Academy of Sciences (CAS), Westlake University and Huazhong University of Science and Technology have demonstrated that by limiting the arrangement of multiple inorganic and organic layers within crystals using a novel technique, they can regulate the energy levels of electrons and holes (positive charge carriers) within perovskites.

This tuning capability affects the materials’ optoelectronic properties and capacity to emit light of specific energies, as illustrated by their ability to function as a laser source.

Researchers from Japan's Tokyo Institute of Technology, University of Oxford in the UK and Colorado State University in the U.S have shown that α-FAPbI₃, a promising solar cell material with a cubic perovskite structure that is metastable at room temperature, can be stabilized by introducing a pseudo-halide ion like thiocyanate (SCN^–) into its structure. The recent findings provide new insights into the stabilization of the α-phase via grain boundary and pseudo-halide engineering.

A material with good photophysical properties that has recently gained momentum is α-formamidinium lead iodide or α-FAPbI₃ (where FA⁺ = CH(NH₂)₂⁺), a crystalline solid with a cubic perovskite structure. Solar cells made of α-FAPbI₃ exhibit a remarkable 25.8% conversion efficiency and an energy gap of 1.48 eV. Unfortunately, α-FAPbI₃ is metastable at room temperature and undergoes a phase transition to δ-FAPbI₃ when triggered by water or light. The energy gap of δ-FAPbI₃ is much larger than the ideal value for solar cell applications, making the preservation of the α-phase crucial for practical purposes. To overcome this problem, the team of researchers, led by Associate Professor Takafumi Yamamoto from Tokyo Institute of Technology (Tokyo Tech), has recently presented a new strategy for stabilizing α-FAPbI₃.

Researchers from Pennsylvania State University have developed a cost-effective method for creating bio-inspired solar devices that could improve the performance of perovskite solar technology. The team drew inspiration from cell membranes, the protective barriers around cells in all living organisms.

The researchers combined perovskite solar cell material with a synthesized version of natural lipid biomolecules to help protect against moisture-induced degradation. These biomolecules are fatty or waxy materials that don’t dissolve in water. The biomolecules formed a membrane-like layer around the perovskite, boosting stability and efficiency in tests. The approach could have a great impact on how perovskite solar cells are designed.

Researchers from the Netherlands' Eindhoven University of Technology, TNO, TNO/Holst Centre and Eindhoven Institute for Renewable Energy Systems (EIRES) have designed a monolithic perovskite-PERC tandem solar cell that utilizes a new type of tunnel recombination junction (TRJ) based on indium tin oxide (ITO), nickel(II) oxide (NiO), and carbazole (2PACz).

The scientists explained that TRJs are usually based on ITO and 2PACz alone, and that the addition of the NiO layer is intended to reduce electrical shunts in the perovskite top cell, due to the inhomogeneity of the 2PACz layer on ITO.

Researchers from The University of Sydney, University of New South Wales, Macquarie University and University of Technology Sydney have demonstrated efficient perovskite solar cells (PSCs) on steel substrates.

The team explained that steel, being flexible and conductive, can itself can act as both a substrate and an electrode for either large-area-monolithic-panel or smaller-area-singular single-junction or multi-junction cell fabrication. The reported cells could be used for building-integrated PV (BIPV), vehicle-integrated solar (VIPV), or other design-integrated photovoltaics for terrestrial or space applications.

Researchers from Chonnam National University, Chinese Academy of Sciences,  Indian Institute of Science (IISc) and Pennsylvania State University have introduced an alternative solar cell design fully based on inorganic perovskites. Their solar cells could be easier to fabricate on a large-scale, while also achieving promising power conversion efficiencies (PCEs).

The key objective of the recent work was to create new solar cells fully based on inorganic perovskites using a developed method that could be easy to up-scale. Ultimately, they fabricated their solar cells using hot-air and thermal evaporation deposition techniques that work at ambient conditions without requiring polar solvents (i.e., liquids containing both positive and negative charges).

Researchers from Harvard University have reported a bioinspired liquid-based encapsulation strategy, that offers protection from water without sacrificing the operational properties of the encapsulated materials.

Using halide perovskite as a model system, the team showed that damage to the perovskite from exposure to water is drastically reduced when it is coated by a polymer matrix with infused hydrophobic oil. 

Researchers from The University of Texas at Austin, University of Pennsylvania and Massachusetts Institute of Technology (MIT) have addressed the question of how lattice dynamics in layered hybrid perovskites are affected by the dimensional engineering of the inorganic frameworks and their interaction with the molecular moieties. 

The team tackled this question by using a combination of spontaneous Raman scattering, terahertz spectroscopy, and molecular dynamics simulations. This approach reveals the structural dynamics in and out of equilibrium and provides unexpected observables that differentiate single- and double-layered perovskites.

Researchers from Duke University and North Carolina State University have reported glass formation for low-melting-temperature 1-MeHa₂PbI₄ (1-MeHa = 1-methyl-hexylammonium) using ultrafast calorimetry, thereby extending the range of metal halide perovskite (MHP) glass formation across a broader range of organic (fused ring to branched aliphatic) and halide (bromide to iodide) compositions. 

A few years ago, Akash Singh and collaborators at Duke University set out to explore the realm of glassy perovskites, a departure from the traditionally studied crystalline perovskites. Since then, this topic sparked interest, resulting in the establishment of a novel research domain centered around glass-forming hybrid perovskite semiconductors with reversible switching. This recent discovery of glass formation in MHPs opens new opportunities associated with reversible glass-crystalline switching, with each state offering distinct optoelectronic properties. However, the previously reported [S-(−)-1-(1-naphthyl)ethylammonium]₂PbBr₄ perovskite is a strong glass former with sluggish glass-crystal transformation time scales, pointing to a need for glassy MHPs with a broader range of compositions and crystallization kinetics.   

A collaborative effort by researchers from the Centre for Hybrid and Organic Solar Energy (CHOSE), Department of Electronic Engineering at Tor Vergata University of Rome, Italy, the Department of Textile Engineering at the University of Guilan, Iran, GreatCell Solar Italia, Institute of Crystallography (IC-CNR), Italy, Department of Biological and Environmental Sciences and Technologies at the University of Salento, Italy and Institute of Nanotechnology (CNR NANOTEC), Italy, has resulted in the development of flexible perovskite solar cells with remarkable power conversion efficiencies (PCE) under white LED illumination.

The team achieved a maximum PCE of 28.9% at an illuminance of 200 lx and a record of 32.5% at 1000 lx, essentially converting a third of the incoming power (note that under 1 sun this figure for perovskite technology is less, i.e. one quarter).