Highly Stable and Moisture-Immune Monocomponent White Perovskite Phosphor by Trifluoromethyl (-CF3) Regulation.

Halide perovskites are emerging as promising candidates for white light solid state lighting. Nevertheless, there are still challenges of a high water stability, a tunable color temperature, and a high photoluminescence quantum yield (PLQY). Herein, we report hydrophobic, electron-withdrawing trifluoromethyl (-CF3)-modified phenethylamine lead bromide (PEA2PbBr4) with ultrahigh stability in water for >2 months, and the broadband white light emission is illustrated by self-trapped excitons attributed to exciton-phonon coupling that coordinate molecular vibration, lattice distortion, and electrostatic interaction. In particular, by Mn2+ doping, the emission color can be tuned from cold (10237 K) to warm (2406 K), and a greatly enhanced PLQY of ≤87.93% can be achieved. Furthermore, the perovskites also possess an excellent color rendering index (the highest is 94). A monocomponent white light-emitting diode with amazing CIE 1931 coordinates of (0.33, 0.32) is further assembled, demonstrating a luminance of 471.5 cd m-2 at 50 mA and good long-term operation stability after >2 months. This study of highly efficient and stable perovskites with high-quality white light emission will open up new opportunities in solid state lighting.

Hydration Intermediate Phase Regulated In-Plane and Out-Plane Epitaxy Growth of Oriented Nano-Array Structures on Perovskite Single Crystals.

Fabrication of organic-metal-halide perovskite micro-nano array structures draws attention to the potential application in polarized light, high-resolution X-ray imaging, light-emitting diodes, and lasers. However, it is still challenging to achieve the growth of controllable long-range ordered nanostructure arrays by chemical solution-based techniques. Herein, controllable epitaxial growth of long-range ordered micro-nano arrays on MAPbI3 single crystal (SC) surface is reported. A hydrated intermediate phase is found that can effectively regulate in-plane and out-plane orientated growth, respectively. This is attributed to the regulation of growth thermodynamics by hydration 0D perovskite intermediate phase enabling free recombination of PbI42- octahedral cages. Further, it is found that the degree of hydration is the key to the realization of in-plane and out-plane growth. Meanwhile, polarization emission and amplified spontaneous emission property are observed in highly oriented nanorod arrays with potential applications in anti-counterfeiting polarized emission.

Thermal Dynamic Self-Healing Supramolecular Dopant Towards Efficient and Stable Flexible Perovskite Solar Cells.

Flexible perovskite solar cells (FPSCs) have attracted great attention due to their advantageous traits such as low cost, portability, light-weight, etc. However, mechanical stability is still the weak point in their practical application. Herein, we prepared efficient FPSCs with remarkable mechanical stability by a dynamic thermal self-healing effect, which can be realized by the usage of a supramolecular adhesive. The supramolecular adhesive, which was obtained by random copolymerization of acrylamide and n-butyl acrylate, is amphiphilic, has a proper glass transition temperature and a high density of hydrogen-bond donors and receptors, providing the possibility of thermal dynamic repair of mechanical damage in FPSCs. The adhesive also greatly improves the leveling property of the precursor solution on the hydrophobic poly[bis(4-phenyl)(2,4,6-trimethylphenyl)]amine (PTAA) surface. PSCs containing this adhesive achieve more than a 20 % power conversion efficiency (PCE) on flexible substrates and a 21.99 % PCE on rigid substrates (certified PCE of 21.27 %), with improved electron mobility and reduced defect concentration.

Enhanced CO catalytic oxidation by Sr reconstruction on the surface of LaxSr1-xCoO3-δ.

Surface electronic structure of solid materials plays a critical role in heterogeneous catalysis. However, surface chemical composition of the perovskite oxides is usually dominated by segregated A-site cations and the amount of oxygen vacancies is relatively low, which seriously restricts their catalytic oxidation property. Here, we prepare perovskite LaxSr1-xCoO3-δ (x=0.3, 0.5, 0.7) with different Sr doping amount and experiment results show that perovskite LSCO with higher content of surface Sr possesses more oxygen vacancies and better catalytic activity. On this basis, we develop a new experimental strategy to create more surface oxygen vacancies to promote their CO catalytic activity. In this method, we use high active hydrogen atoms (BH4-) as reductant to realize surface in-situ chemical composite modification of LaxSr1-xCoO3-δ (x=0.3, 0.5, 0.7), which causes their surface reconstruction (surface Sr enrichment). The regulation mainly focuses on the atomic layer level without damaging their bulk phase structure. Different from traditional high temperature annealing under reducing atmosphere, this method is high-efficiency, green and controllable. Furthermore, we study the surface reconstruction process and demonstrated that it is atomic layer engineering on the surface of LaxSr1-xCoO3-δ (x=0.3, 0.5, 0.7) by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS). Our experiment results also show that these samples treated by this method exhibit superior activity for CO oxidation compared with original samples.

Defect Engineering, Electronic Structure, and Catalytic Properties of Perovskite Oxide La0.5 Sr0.5 CoO3-δ.

The electronic structures of transition metal oxides play a crucial role in the physical and chemical properties of solid materials. Defect engineering is an efficient way to regulate the electronic structure and improve the performance of materials. Here, we develop a defect engineering route that is implemented by controlling the topochemical reactions between cobalt perovskite and urea to optimize the electronic structure of La0.5 Sr0.5 CoO3-δ (LSCO). Urea pyrolysis is able to increase the oxygen defect concentration and cause octahedral distortions. Furthermore, we can distinctly observe that the introduction of oxygen vacancies narrows the hybridization orbital between O 2p and Co 3d and optimizes the O p-band center near the Fermi level by X-ray absorption spectroscopy, which greatly improves the catalytic activity of CO oxidation and photocatalytic water splitting. These results highlight the relationship between oxygen defects, electronic structure, and catalytic activity of perovskite LSCO, and demonstrate a rational approach to defect design and reveal the importance of anion redox chemistry for the structures and properties of perovskite oxides.