High stability and strong luminescence CsPbBr3-Cs4PbBr6 thin films for all-inorganic perovskite light-emitting diodes

All-inorganic lead halide perovskite, characterized by its exceptional optical and electrical properties, is burgeoning as a potential optoelectronic material. However, the standalone CsPbBr3 component encounters several challenges including small exciton binding energy (≈40 meV) and long charge diffusion length, giving rise to low photo-luminescence quantum-yield (PLQY); ion migration leads to instability in device operation, hindering device operation and potential development. To circumvent these limitations, our research endeavors to construct a novel core-shell structure that transforms the continuous [PbX6]4- octahedron into an isolated octahedral structure. We introduce the Cs4PbBr6 phase with 0D structure to passivate the vacancy defects in CsPbBr3, thereby suppressing ion migration and enhancing the luminescence intensity and stability. Our methodology involves fabricating dense CsPbBr3-Cs4PbBr6 composite films using a co-evaporation method, wherein the molar ratio of CsBr and PbBr2 is precisely adjusted. The films are subsequently rapidly annealed under ambient air conditions, and the effects of different annealing temperatures and annealing times on the CsPbBr3-Cs4PbBr6 films were investigated. Our results demonstrate significantly improved stability of the annealed films, with a mere 15% decrease in PL intensity after 100 days of storage under ambient air conditions at 48% relative humidity (RH). Based on this thin film, we fabricated all-inorganic structure Ag/N-Si/CsPbBr3-Cs4PbBr6/NiO/ITO light emitting diodes (LEDs), the devices have a low turn-on voltage VT ∼3 V and under unencapsulated, ambient air conditions, it can operate continuously for 12 hours under DC drive with only 10% attenuation. The results we obtained open up the possibility of designing and developing air-stable perovskite LEDs.

Riemannian Surface on Carbon Anodes Enables Li-Ion Storage at -35 °C

Since sluggish Li⁺ desolvation leads to severe capacity degradation of carbon anodes at subzero temperatures, it is urgently desired to modulate electron configurations of surface carbon atoms toward high capacity for Li-ion batteries. Herein, a carbon-based anode material (O-DF) was strategically synthesized to construct the Riemannian surface with a positive curvature, which exhibits a high reversible capacity of 624 mAh g^-1 with an 85.9% capacity retention at 0.1 A g^-1 as the temperature drops to -20 °C. Even if the temperature drops to -35 °C, the reversible capacity is still effectively retained at 160 mAh g^-1 after 200 cycles. Various characterizations and theoretical calculations reveal that the Riemannian surface effectively tunes the low-temperature sluggish Li⁺ desolvation of the interfacial chemistry via locally accumulated charges of non-coplanar sp ^x (2 < x < 3) hybridized orbitals to reduce the rate-determining step of the energy barrier for the charge-transfer process. Ex-situ measurements further confirm that the sp ^x -hybridized orbitals of the pentagonal defect sites should denote more negative charges to solvated Li⁺ adsorbed on the Riemannian surface to form stronger Li-C coordinate bonds for Li⁺ desolvation, which not only enhances Li-adsorption on the curved surface but also results in more Li⁺ insertion in an extremely cold environment.

Modelling cascading failures in networks with the harmonic closeness

Many studies on cascading failures adopt the degree or the betweenness of a node to define its load. From a novel perspective, we propose an approach to obtain initial loads considering the harmonic closeness and the impact of neighboring nodes. Based on simulation results for different adjustable parameter θ, local parameter δ and proportion of attacked nodes f, it is found that in scale-free networks (SF networks), small-world networks (SW networks) and Erdos-Renyi networks (ER networks), there exists a negative correlation between optimal θ and δ. By the removal of the low load node, cascading failures are more likely to occur in some cases. In addition, we find a valuable result that our method yields better performance compared with other methods in SF networks with an arbitrary f, SW and ER networks with large f. Moreover, the method concerning the harmonic closeness makes these three model networks more robust for different average degrees. Finally, we perform the simulations on twenty real networks, whose results verify that our method is also effective to distribute the initial load in different real networks.

The lattice reconstruction of Cs-introduced FAPbI1.80Br1.20 enables improved stability for perovskite solar cells

Inorganic-organic hybrid perovskite solar cells (PSCs) have stirred up a new research spree in the field of photovoltaics due to its high photoelectric conversion efficiency and simple preparation process. In recent years, the research of inorganic-organic hybrid PSCs has been widely reported, among which FA+/Cs+ PSCs are especially outstanding. However, there are few reports explaining the lattice structural change mechanism of Cs x FA1-x PbI1.80Br1.20 PSCs from the view of chemical bonds. In this work, a facile method of 15% Cs+ cations partially substituting FA+ cations has been presented to enhance the structural stability and photovoltaic performances of FAPbI1.80Br1.20 PSCs. The partial incorporation of Cs+ in FAPbI1.80Br1.20 resulted in a more beneficial tolerance factor and inhibited the deep defect state of elemental Pb. More importantly, it inhibited the phase transition from the cubic black α-phase to the hexagonal yellow δ-phase of FAPbI1.80Br1.20. Moreover, the power conversion efficiency (PCE) of Cs0.15FA0.85PbI1.80Br1.20 PSCs achieved a substantial improvement. The stability also achieved a remarkable promotion, which was demonstrated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Nuclear Magnetic Resonance (NMR). These analyses indicate that 15% Cs+ can induce the lattice shrinkage, reduce the specific traps and inhibit the phase transition, thus improving the structural stabilities of Cs0.15FA0.85PbI1.80Br1.20 PSCs under atmosphere and calefaction. These results provide an effective way for fabricating stable and efficient inorganic-organic perovskite solar cells with promising properties.