Improve the Charge Carrier Transporting in Two-Dimensional Ruddlesden-Popper Perovskite Solar Cells.

Conventional 3D organic-inorganic halide perovskite materials have shown substantial potential in the field of optoelectronics, enabling the power conversation efficiency of solar cells beyond 26%. A key challenge limiting the further commercial application of 3D perovskite solar cells is their inherent instability over outer oxygen, humidity, light, and heat. By contrast, 2D Ruddlesden-Popper (2DRP) perovskites with bulky organic cations can effectively stabilize the inorganic slabs, yielding excellent environmental stability. However, the efficiencies of 2DRP perovskite solar cells are much lower than those of the 3D counterparts due to poor charge carrier transporting property of insulating bulky organic cations. Their inner structural, dielectric, optical, and excitonic properties remain to be primarily studied. In this review, the main reasons for the low efficiency of 2DRP perovskite solar cells are first analyzed. Next, a detailed description of various strategies for improving the charge carrier transporting of 2DRP perovskites is provided, such as bandgap regulation, perovskite crystal phase orientation and distribution, energy level matching, interfacial modification, etc. Finally, a summary is given, and the possible future research directions and methods to achieve high-efficiency and stable 2DRP perovskite solar cells are rationalized.

Promoting Ruddlesden-Popper Perovskite Formation by Tailoring Spacer Intramolecular Interaction for Efficient and Stable Solar Cells.

Low-dimensional Ruddlesden-Popper phase (LDRP) perovskites are widely studied in the field of photovoltaics due to their tunable energy-band properties, enhanced photostability, and improved environmental stability compared to the 3D perovskites. However, the insulating spacers with weak intramolecular interaction used in LDRP materials limit the out-of-plane charge transport, leading to poor device performance of LDRP perovskite solar cells (PSCs). Here, a functional ligand, 3-guanidinopropanoic acid (GPA), which is capable of forming strong intramolecular hydrogen bonds through the carboxylic acid group, is employed as an organic spacer for LDRP PSCs. Owing to the strong interaction between GPA molecules, high-quality LDRP (GPA)2(MA)n-1PbnI3n+1 film with promoted formation of n = 5 phase, improved crystallinity, preferential vertical growth orientations, reduced trap-state density, and prolonged carrier lifetime is achieved using GPAI as the dimensionality regulator compared to butylamine hydroiodide (BAI). As a result, GPA-based LDRP PSC exhibits a champion power conversion efficiency of 18.16% that is much superior to the BA-based LDRP PSC (15.43%). Importantly, the optimized GPA-based LDRP PSCs without encapsulation show enhanced illumination, thermal, storage, and humidity stability compared to BA-based ones. This work provides new insights into producing high n value LDRP films and their efficient and stable PSCs.

Enhancing Energy Storage Performance in Lead-Free Bismuth Sodium Niobate-Based Tungsten Bronze Ceramics through Relaxor Tuning.

A series of tungsten bronze Sr2Na0.85Bi0.05Nb5-xTaxO15 (SBNN-xTa) ferroelectric ceramics were designed and synthesized by the traditional solid-phase reaction method. The B-site engineering strategy was utilized to induce structural distortion, order-disorder distribution, and polarization modulation to enhance relaxor behavior. Through investigating the impact of B-site Ta replacement on the structure, relaxor behavior, and energy storage performance, this study has shed light on the two main factors for relaxor nature: (1) with the increase of Ta substitution, the tungsten bronze crystal distortion and expansion induced the structural change from an orthorhombic Im2a phase to Bbm2 phase at room temperature; (2) the transition from ferroelectric to relaxor behavior could be attributed to the coordinate incommensurate local superstructural modulations and the generation of nanodomain structure regions. Moreover, we benefited from the effective decrease of ceramic grains and inhibition of abnormal growth. Finally, we obtained an effective energy storage density (Wrec) ∼ 1.6 J/cm3, an efficiency (η) ∼ 80%, a current density (CD) ∼ 1384.2 A/cm2, and a power density (PD) ∼ 138.4 MW/cm3.

Microvolt T-wave alternans for risk stratification of cardiac events in ischemic cardiomyopathy: a meta-analysis.

BACKGROUND: The ability of microvolt T-wave alternans (MTWA) for risk stratification of cardiac events in patients with ischemic cardiomyopathy (ICM) has not been well established. METHODS: The authors systematically reviewed current literature and carried out a meta-analysis to determine the ability of MTWA to predict the outcome severity after ICM. Major endpoints include composite endpoint of cardiac mortality and severe arrhythmic events in primary prevention of patients with ICM, as well as all-cause mortality (cardiac death, and/or non-cardiac death). RESULTS: Seven trials were included by using MTWA for risk stratification of cardiac events in 3385 patients with ICM. All patients were distributed into two groups according to the results of MTWA tests: non-negative group included positive and indeterminate, and negative group. Compared with the negative group, non-negative group showed increased rates of cardiac mortality or severe arrhythmic events (RR=1.65, 95%CrI=1.32, 2.071), sudden cardiac death (SCD) (RR=2.04 95%CrI=1.11, 3.75), and all-cause mortality (RR=2.11, 95%CrI=1.60, 2.79). The funnel plot revealed that there might be bias within current publications. The fail-safe number of composite endpoint and all-cause mortality was 14.42 and 18.93, respectively (when P=0.01). The fail-safe number of SCD was 1.07 (when P=0.05), which may be caused by the small case number of included studies and some patients with ICD included. CONCLUSIONS: The non-negative group of MTWA had a nearly double risk of severe outcomes compared with the negative group. Therefore, MTWA represents a potential useful tool for judging the severity of ICM.

Multifunctional carbon nanotubes for direct electrochemistry of glucose oxidase and glucose bioassay.

Polydopamine (Pdop) has recently been shown to adsorb to a wide variety of surfaces and serves as an adhesion layer to immobilize biological molecules. In this work, the multifunctional carbon nanotube (CNT) composites were prepared though the oxidation of dopamine at room temperature and subsequent electroless silver deposition by mildly stirring. The stable immobilization and direct electron transfer of glucose oxidase were achieved on the composite film modified glassy carbon electrode. The resulting electrode gave a well-defined redox peaks with a formal potential of about -482 mV (vs. SCE) in pH 7.0 buffer. The electron transfer rate constant was estimated to be 3.6 s(-1), due to the combined contribution of Pdop, CNTs and Ag nanoparticles with the help of Nafion. Furthermore, the method for detecting of glucose was proposed based on the decrease of oxygen caused by the enzyme-catalyzed reaction between glucose oxidase (GOD) and glucose. The linear response to glucose ranging from 50.0 µM to 1.1 mM (R(2)=0.9958), with a calculated detection limit of 17.0 µM at a signal-to-noise ratio of 3. The low calculated apparent Michaelis-Menten constant (K(M)(app)) was 5.46 mM, implying the high enzymatic activity and affinity of immobilized GOD for glucose. It can reasonably be expected that this observation might hold true for other noble metal nanostructure-electroactive protein systems, providing a promising platform for the development of biosensors and biofuel cells.