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See detailRoadmap on organic–inorganic hybrid perovskite semiconductors and devices
Schmidt-Mende, Lukas; Dyakonov, Vladimir; Olthof, Selina et al

in APL Materials (2021)

Metal halide perovskites are the first solution processed semiconductors that can compete in their functionality with conventional semiconductors, such as silicon. Over the past several years, perovskite ... [more ▼]

Metal halide perovskites are the first solution processed semiconductors that can compete in their functionality with conventional semiconductors, such as silicon. Over the past several years, perovskite semiconductors have reported breakthroughs in various optoelectronic devices, such as solar cells, photodetectors, light emitting and memory devices, and so on. Until now, perovskite semiconductors face challenges regarding their stability, reproducibility, and toxicity. In this Roadmap, we combine the expertise of chemistry, physics, and device engineering from leading experts in the perovskite research community to focus on the fundamental material properties, the fabrication methods, characterization and photophysical properties, perovskite devices, and current challenges in this field. We develop a comprehensive overview of the current state-of-the-art and offer readers an informed perspective of where this field is heading and what challenges we have to overcome to get to successful commercialization. [less ▲]

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See detailCrossover between distinct symmetries in solid solutions of rare earth nickelates
Fowlie, Jennifer; Mundet, Bernat; Toulouse, Constance UL et al

in APL MATERIALS (2021), 9(8),

A strong coupling of the lattice to functional properties is observed in many transition metal oxide systems, such as the ABO(3) perovskites. In the quest for tailor-made materials, it is essential to be ... [more ▼]

A strong coupling of the lattice to functional properties is observed in many transition metal oxide systems, such as the ABO(3) perovskites. In the quest for tailor-made materials, it is essential to be able to control the structural properties of the compound(s) of interest. Here thin film solid solutions that combine NdNiO3 and LaNiO3, two materials with the perovskite structure but distinct space groups, are analyzed. Raman spectroscopy and scanning transmission electron microscopy are combined in a synergistic approach to fully determine the mechanism of the structural crossover with chemical composition. It is found that the symmetry transition is achieved by phase coexistence in a way that depends on the substrate selected. These results carry implications for analog-tuning of physical properties in future functional materials based on these compounds. [less ▲]

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See detailThe other model antiferroelectric: PbHfO3 thin films from ALD precursors
Hanrahan, Brendan; Milesi-Brault, Cosme; Leff, Asher et al

in APL MATERIALS (2021), 9(2),

Antiferroelectric PbHfO3 is grown from atomic layer deposition precursors lead bis(dimethylaminomethylpropanolate) and tetrakis dimethylamino hafnium with H2O and O-3 oxidizers in thicknesses from 20 nm ... [more ▼]

Antiferroelectric PbHfO3 is grown from atomic layer deposition precursors lead bis(dimethylaminomethylpropanolate) and tetrakis dimethylamino hafnium with H2O and O-3 oxidizers in thicknesses from 20 nm to 200 nm at a substrate temperature of 250 degrees C. X-ray analysis shows an as-grown crystalline PbO phase that diffuses into an amorphous HfO2 matrix upon annealing to form a randomly oriented, orthorhombic PbHfO3 thin film. Electrical characterization reveals characteristic double hysteresis loops with maximum polarizations of around 30 mu C/cm(2) and transition fields of 350 kV/cm-500 kV/cm depending on the thickness. Temperature-dependent permittivity and polarization testing show a phase transition at 185 degrees C, most probably to the paraelectric phase, but give no clear evidence for the intermediate phase known from bulk PbHfO3. The energy storage density for the films reaches 16 J/cm(3) at 2 MV/cm. A dielectric tunability of 221 is available within 1 V for the thinnest film. These results highlight the unique spectrum of properties available for thin film perovskite antiferroelectrics. [less ▲]

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See detailVibrational properties of LaNiO3 films in the ultrathin regime
Schober, Alexander; Fowlie, Jennifer; Guennou, Mael UL et al

in APL MATERIALS (2020), 8(6),

Collective rotations and tilts of oxygen polyhedra play a crucial role in the physical properties of complex oxides such as magnetism and conductivity. Such rotations can be tuned by preparing thin films ... [more ▼]

Collective rotations and tilts of oxygen polyhedra play a crucial role in the physical properties of complex oxides such as magnetism and conductivity. Such rotations can be tuned by preparing thin films in which dimensionality, strain, and interface effects come into play. However, little is known of the tilt and rotational distortions in films a few unit cells thick including the question of if coherent tilt patterns survive at all in this ultrathin limit. Here, a series of films of perovskite LaNiO3 is studied and it is shown that the phonon mode related to oxygen octahedral tilts can be followed by Raman spectroscopy down to a film thickness of three pseudocubic perovskite unit cells (similar to 1.2 nm). To push the limits of resolution to the ultrathin regime, a statistical analysis method is introduced to separate the Raman signals of the film and substrate. Most interestingly, these analyses reveal a pronounced hardening of the tilt vibrational mode in the thinnest films. A comparison between the experimental results, first principles simulations of the atomic structure, and the standing wave model, which accounts for size effects on the phononic properties, reveals that in the ultrathin regime, the Raman spectra are a hybrid entity of both the bulk and surface phononic behavior. These results showcase Raman spectroscopy as a powerful tool to probe the behavior of perovskite films down to the ultrathin limit. [less ▲]

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See detailRole of the ferroelastic strain in the optical absorption of BiVO4
Hill, Christina; Weber, Mads C.; Lehmann, Jannis et al

in APL MATERIALS (2020), 8(8),

Bismuth vanadate (BiVO4) has recently been under focus for its potential use in photocatalysis thanks to its well-suited absorption edge in the visible light range. Here, we characterize the optical ... [more ▼]

Bismuth vanadate (BiVO4) has recently been under focus for its potential use in photocatalysis thanks to its well-suited absorption edge in the visible light range. Here, we characterize the optical absorption of a BiVO4 single crystal as a function of temperature and polarization direction by reflectance and transmittance spectroscopy. The optical bandgap is found to be very sensitive to the temperature, and to the tetragonal-to-monoclinic ferroelastic transition at 523 K. The anisotropy, as measured by the difference in the absorption edge for the light polarized parallel and perpendicular to the principal axis, is reduced from 0.2 eV in the high-temperature tetragonal phase to 0.1 eV at ambient temperature. We show that this evolution is dominantly controlled by the ferroelastic shear strain. These findings provide a route for further optimization of bismuth vanadate-based light absorbers in photocatalytic devices. [less ▲]

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