Volume 13 Issue 9, September 2014

The rise of metal halide perovskites as light harvesters has stunned the photovoltaic community. As the efficiency race continues, questions on the control of the performance of perovskite solar cells and on its characterization are being addressed.

The epitaxial growth of oxide heterostructures is generally thought to occur in a deterministic fashion. Recent results on the Ruddlesden–Popper phases show this is not always the case, and that a dynamic rearrangement of the layers during growth can spring up surprises.

The dream of printing highly efficient solar cells is closer than ever to being realized. Solvent engineering has enabled the deposition of uniform perovskite semiconductor films that yield greater than 15% power-conversion efficiency.

The optical properties of self-assembled plasmonic nanoparticles can be reversibly tuned by using DNA strands.

Membrane-based acoustic resonators of subwavelength dimensions achieve nearly perfect acoustic absorption.

Inspired by the chemistry of adhesive proteins in mussels, hydrogels can now be made to self-heal in water without the aid of metal chelates.

Three-dimensional Dirac semimetals such as Cd₃As₂ are attracting attention because their electronic structure can be considered to be the three-dimensional analogue of graphene’s. Low-temperature scanning tunnelling measurements of the 112 cleavage plane of Cd₃As₂ now reveal its electronic structure down to atomic length scales, as well as its Landau spectrum and quasiparticle interference pattern.

The electronic and structural components of charge density waves occurring in layered transition metal dichalcogenides are known to be interdependent, yet have only been probed in separate measurements. Now, a broadband terahertz spectroscopy approach that monitors the evolution of these two order parameters simultaneously is demonstrated.

Until now, it has not been possible to switch chirality in plasmonic nanostructures at will and repeatedly. Now, thanks to DNA-regulated conformational changes, reconfigurable 3D plasmonic metamolecules with switchable chirality have been created.

Synthetic polymers functionalized with mussel-inspired catechols have been shown to exhibit self-healing and adhesive properties, mediated by metal chelation, that are much needed in biomedical and environmental applications. Now, a metal-free approach to complete polymer self-healing underwater mediated by extensive hydrogen bonding in catechol-functionalized polyacrylates is reported.

Acoustic impedance-matched surfaces do not reflect incident waves. Traditional means of acoustic absorption have so far resulted in imperfect impedance matching and bulky structures, or require costly and sophisticated electrical design. Inspired by electromagnetic metamaterials, a subwavelength acoustically reflecting surface with hybrid resonances and impedance-matched to airborne sound at tunable frequencies is now demonstrated.

Although the Ruddlesden–Popper series of compounds offer a range of appealing properties, their fabrication in thin-film form has been challenging. Using molecular beam epitaxy, layered oxide films of this family are synthesized, and shown to undergo a dynamical rearrangement during the growth process.

Many catalytic reactions exhibit oscillatory behaviour but these oscillations are not well understood for catalysts consisting of supported nanoparticles. The study of oscillatory CO oxidation catalysed by Pt nanoparticles now reveals that periodic changes in the CO oxidation are synchronous with a periodic refacetting of the Pt nanoparticles.

For high-power white-light-emitting diodes (LEDs) to become a technological reality there is a need to find more efficient red-emitting phosphor materials. Eu²⁺-doped Sr[LiAl₃N₄], a member of the nitridoaluminates compound class, is now proved to be a high-performance narrow-band red-emitting phosphor material that can be easily coupled with existing GaN-based blue-LED technology for use in white LEDs.

The performance of solar cells based on organic–inorganic perovskites strongly depends on the device architecture and processing conditions. It is now shown that solvent engineering enables the deposition of very dense perovskite layers on mesoporous titania, leading to photovoltaic devices with a high light-conversion efficiency and no hysteresis.

Nanoparticle-based fluorescence imaging does not usually allow cell membrane-bound particles and intracellular particles to be distinguished from each other. Now, using functionalized silver nanoparticles as plasmonic probes, this distinction can be made following a rapid, non-toxic etching process that selectively removes the extracellular nanoparticles but leaves the intracellular nanoparticles unharmed.

The rapid efficiency increase of solar cells based on perovskites makes these materials promising contenders in cheap devices for solar energy harvesting. This focus issue highlights performance improvements in perovskite photovoltaics, and discusses some of the challenges to bring these devices to the market.