Low dimensional lead halide perovskites have attracted huge research interest due to their structural diversity and remarkable photophysical properties. The ability to controllably change dimensionality/structure of perovskites remains highly challenging. Here, we report synthetic control on structure/ dimensionality of ethylenediammonium (ED) lead bromide perovskite from a two dimensionally networked (2DN) sheet to a one dimensionally networked (1DN) chain structure. Intercalation of solvent molecules into the perovskite plays a crucial role in directing the final dimensionality/structure. This change in dimensionality reflects strongly in the observed differences in photophysical properties. Upon UV excitation, the 1DN structure emits white light due to easily formed "self-trapped" excitons. 2DN perovskites show band edge blue emission (∼410 nm). Interestingly, Mn 2+ incorporated 2DN perovskites show a highly red-shif ted Mn 2+ emission peak at ∼670 nm. Such a long wavelength Mn 2+ emission peak is unprecedented in the perovskite family. This report highlights the synthetic ability to control the dimensionality/structure of perovskite and consequently its photophysical properties.
Perovskite light-emitting
diodes have almost reached the threshold
for potential commercialization within a few years of research. However,
there are still some unsolved puzzles such as large ideality factor
and the presence of large negative capacitance especially at the low-frequency
regime yet to be addressed. Here, we have fabricated a methylammonium
lead tri-bromide perovskite n–i–p structure for light-emitting
diodes from a smooth and textured emissive layer and demonstrated
for the first time that these two factors are strongly dependent on
the perovskite film morphology. Bias-dependent capacitance measurement
also reveals the transition between negative to positive capacitance
in textured films at the low-frequency regime. We have observed an
anomalous capacitive behavior at the mid-frequency regime in smooth
perovskite films but not in textured films. The relatively large ideality
factor and anomalous capacitive behavior observed in perovskite light-emitting
diodes are due to the presence of strong coupling between ions and
electrons near the electrode interface. Therefore, the ideality factor
and anomalous capacitance at the mid-frequency regime can be decreased
by minimizing electronic–ionic coupling in textured perovskite
films, while light outcoupling can be improved significantly.
Effects of substitutions of rare earth (RE) elements (Y, La, Ce, and Nd) to the Zr-based AB 2 multi-phase metal hydride (MH) alloys on the structure, gaseous phase hydrogen storage (H-storage), and electrochemical properties were studied and compared. Solubilities of the RE atoms in the main Laves phases (C14 and C15) are very low, and therefore the main contributions of the RE additives are through the formation of the RENi phase and change in TiNi phase abundance. Both the RENi and TiNi phases are found to facilitate the bulk diffusion of hydrogen but impede the surface reaction. The former is very effective in improving the activation behaviors.´40˝C performances of the Ce-doped alloys are slightly better than the Nd-doped alloys but not as good as those of the La-doped alloys, which gained the improvement through a different mechanism. While the improvement in ultra-low-temperature performance of the Ce-containing alloys can be associated with a larger amount of metallic Ni-clusters embedded in the surface oxide, the improvement in the La-containing alloys originates from the clean alloy/oxide interface as shown in an earlier transmission electron microscopy study. Overall, the substitution of 1 at% Ce to partially replace Zr gives the best electrochemical performances (capacity, rate, and activation) and is recommended for all the AB 2 MH alloys for electrochemical applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.