Nonmonotonic Photostability of BA2MAn-1PbnI3n+1 Homologous Layered Perovskites

Development of Quasi-Two-Dimensional Perovskites and Their Application in Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) perovskites have attracted much attention due to their outstanding properties, such as inherent quantum-well structure, strong dielectric and quantum confinement, large exciton binding energy, and high photoluminescence quantum yield. By virtue of these superior merits, quasi-2D perovskites have shown great potential for next-generation light-emitting diodes (LEDs). Herein, this review presents an overview of the basic properties of quasi-2D perovskites and their photoluminescence modulations by large organic cation engineering, monovalent cation engineering, halogen engineering, defect passivation engineering, and dimensionality engineering. Furthermore, the strategies of charge-transport layer optimization, interfacial engineering, light-outcoupling efficiency improvement, and operating stability improvement are summarized for fabricating high-performance quasi-2D perovskite LEDs (PeLEDs). Finally, the challenges and outlook for the future development of quasi-2D PeLEDs are unambiguously proposed.

Synergy of 3D and 2D Perovskites for Durable, Efficient Solar Cells and Beyond

Three-dimensional (3D) organic-inorganic lead halide perovskites have emerged in the past few years as a promising material for low-cost, high-efficiency optoelectronic devices. Spurred by this recent interest, several subclasses of halide perovskites such as two-dimensional (2D) halide perovskites have begun to play a significant role in advancing the fundamental understanding of the structural, chemical, and physical properties of halide perovskites, which are technologically relevant. While the chemistry of these 2D materials is similar to that of the 3D halide perovskites, their layered structure with a hybrid organic-inorganic interface induces new emergent properties that can significantly or sometimes subtly be important. Synergistic properties can be realized in systems that combine different materials exhibiting different dimensionalities by exploiting their intrinsic compatibility. In many cases, the weaknesses of each material can be alleviated in heteroarchitectures. For example, 3D-2D halide perovskites can demonstrate novel behavior that neither material would be capable of separately. This review describes how the structural differences between 3D halide perovskites and 2D halide perovskites give rise to their disparate materials properties, discusses strategies for realizing mixed-dimensional systems of various architectures through solution-processing techniques, and presents a comprehensive outlook for the use of 3D-2D systems in solar cells. Finally, we investigate applications of 3D-2D systems beyond photovoltaics and offer our perspective on mixed-dimensional perovskite systems as semiconductor materials with unrivaled tunability, efficiency, and technologically relevant durability.

Butanediammonium Salt Additives for Increasing Functional and Operando Stability of Light-Harvesting Materials in Perovskite Solar Cells

Organic diammonium cations are a promising component of both layered (2D) and conventional (3D) hybrid halide perovskites in terms of increasing the stability of perovskite solar cells (PSCs). We investigated the crystallization ability of phase-pure 2D perovskites based on 1,4-butanediammonium iodide (BDAI2) with the layer thicknesses n = 1, 2, 3 and, for the first time, revealed the presence of a persistent barrier to obtain BDA-based layered compounds with n > 1. Secondly, we introduced BDAI2 salt into 3D lead−iodide perovskites with different cation compositions and discovered a threshold-like nonmonotonic dependence of the perovskite microstructure, optoelectronic properties, and device performance on the amount of diammonium additive. The value of the threshold amount of BDAI2 was found to be ≤1%, below which bulk passivation plays the positive effect on charge carrier lifetimes, fraction of radiative recombination, and PSCs power conversion efficiencies (PCE). In contrast, the presence of any amount of diammonium salt leads to the sufficient enhancement of the photothermal stability of perovskite materials and devices, compared to the reference samples. The performance of all the passivated devices remained within the range of 50 to 80% of the initial PCE after 400 h of continuous 1 sun irradiation with a stabilized temperature of 65 °C, while the performance of the control devices deteriorated after 170 h of the experiment.

Rapidly expanding spin-polarized exciton halo in a two-dimensional halide perovskite at room temperature

Monitoring of the spatially resolved exciton spin dynamics in two-dimensional semiconductors has revealed the formation of a spatial pattern and long-range transport of the spin-polarized excitons, which holds promise for exciton-based spin-optoelectronic applications. However, the spatial evolution has been restricted to cryogenic temperatures because of the short exciton spin relaxation times at room temperature. Here, we report that two-dimensional halide perovskites can overcome this limitation owing to their relatively long exciton spin relaxation times and substantial exciton-exciton interactions. We demonstrate the emergence of a halo-like spatial profile in spin-polarized exciton population and its ultrafast expansion at room temperature by performing time-resolved Faraday rotation imaging of spin-polarized excitons in two-dimensional perovskite (C₄H₉NH₃)₂(CH₃NH₃)₃Pb₄I₁₃. Exciton-exciton exchange interactions induce density-dependent nonlinear relaxation and ultrafast transport of exciton spins and give rise to a rapidly expanding halo-like spatial pattern. The density-dependent spatial control suggests the potential of using two-dimensional halide perovskites for spin-optoelectronic applications.

Supramolecular Diiodine-Bromostannate(IV) Complexes: Narrow Bandgap Semiconductors

Three supramolecular bromostannates(IV) with "trapped" diiodine molecules, Cat₂{[SnBr₆](I₂)} (Cat = Me₄N⁺ (1), 1-MePy⁺ (2) and 4-MePyH (3)), were synthesized. In all cases, I₂ linkers are connected with bromide ligands via halogen···halogen non-covalent interactions. Articles 1-3 were studied using Raman spectroscopy, thermogravimetric analysis, and diffuse reflectance spectroscopy. The latter indicates that 1-3 are narrow band gap semiconductors.

Triphenyllead Hydroperoxide: A 1D Coordination Peroxo Polymer, Single-Crystal-to-Single-Crystal Disproportionation to a Superoxo/Hydroxo Complex, and Application in Catalysis

The synthesis, transformation, and application in catalysis of triphenyllead hydroperoxide, the first dioxygen lead complex, are described. Triphenyllead hydroperoxide is characterized by ²⁰⁷Pb nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and single-crystal X-ray diffraction, revealing the first one-dimensional (1D) coordination peroxo polymer. Photolytic isomorphous transformation of Ph₃PbOOH yields a mixed hydroxo/superoxo crystalline structure, the first nonalkali superoxo crystalline metal salt, which is stable up to 100 °C. Upon further photolysis, another isomorphous transformation of the superoxide to hydroxide is observed. These are the first single-crystal-to-single-crystal hydroperoxide-to-superoxide and then to hydroxide transformations reported to date. Photolysis of triphenyllead hydroperoxide yields two forms of superoxide-doped crystalline structures that are distinguished by widely different characteristic relaxation times. The use of Ph₃PbOOH as an easy-to-handle solid two-electron oxidant for the highly enantioselective epoxidation of olefins is described.