A Comparative Study of Light‐Emitting Diodes Based on All‐Inorganic Perovskite Nanoparticles (CsPbBr3) Synthesized at Room Temperature and by a Hot‐Injection Method

Perovskite nanoparticles (PeNPs) have been extensively studied for optoelectronic applications, owing to their extremely high photoluminescence quantum yield, tunable band gap, and exceptionally narrow emission spectra. Therefore, PeNPs are considered excellent candidates for the development of high‐efficiency, low‐cost, wide‐gamut, and high‐purity color displays. However, their synthesis typically involves multistep cumbersome processes that might hinder commercial development. Herein, green light‐emitting diodes (LEDs) prepared by using all‐inorganic PeNPs CsPbBr3 synthesized at room temperature (RT) are reported and their performance compared with those prepared by a traditional hot‐injection method. Insights into the morphology and optoelectronic properties of RT PeNPs are provided through AFM and TEM and employing them in LEDs

Research Update: Behind the high efficiency of hybrid perovskite solar cells

Perovskite solar cells (PSCs) marked tremendous progress in a short period of time and offer bright hopes for cheap solar electricity. Despite high power conversion efficiency >20%, its poor operational stability as well as involvement of toxic, volatile, and less-abundant materials hinders its practical deployment. The fact that degradation and toxicity are typically observed in the most successful perovskite involving organic cation and toxic lead, i.e., CH3NH3PbX3, requires a deep understanding of their role in photovoltaic performance in order to envisage if a non-toxic, stable yet highly efficient device is feasible. Towards this, we first provide an overview of the basic chemistry and physics of halide perovskites and its correlation with its extraordinary properties such as crystal structure, bandgap, ferroelectricity, and electronic transport. We then discuss device related aspects such as the various device designs in PSCs and role of interfaces in origin of PV parameters particularly open circuit voltage, various film processing methods and their effect on morphology and characteristics of perovskite films, and the origin and elimination of hysteresis and operational stability in these devices. We then identify future perspectives for stable and efficient PSCs for practical deployment

Quantification of Ion Migration in CH3NH3PbI3 Perovskite Solar Cells by Transient Capacitance Measurements

Solar cells based on organic-inorganic metal halide perovskites show efficiencies close to highly-optimized silicon solar cells. However, ion migration in the perovskite films leads to device degradation and impedes large scale commercial applications. We use transient ion-drift measurements to quantify activation energy, diffusion coefficient, and concentration of mobile ions in methylammonium lead triiodide (MAPbI3) perovskite solar cells, and find that their properties change close to the tetragonal-to-orthorhombic phase transition temperature. We identify three migrating ion species which we attribute to the migration of iodide (I-) and methylammonium (MA+). We find that the concentration of mobile MA+ ions is one order of magnitude higher than the one of mobile I- ions, and that the diffusion coefficient of mobile MA+ ions is three orders of magnitude lower than the one for mobile I- ions. We furthermore observe that the activation energy of mobile I- ions (0.29 eV) is highly reproducible for different devices, while the activation energy of mobile MA+ depends strongly on device fabrication. This quantification of mobile ions in MAPbI3 will lead to a better understanding of ion migration and its role in operation and degradation of perovskite solar cells

Humidity Versus Photo-Stability of Metal Halide Perovskite Films in a Polymer Matrix

Despite the high efficiency of over 21% reported for emerging thin film perovskite solar cells, one of the key issues prior to their commercial deployment is to attain their long term stability under ambient and outdoor conditions. The instability in perovskite is widely conceived to be humidity induced due to the water solubility of its initial precursors, which leads to decomposition of the perovskite crystal structure; however, we note that humidity alone is not the major degradation factor and it is rather the photon dose in combination with humidity exposure that triggers the instability. In our experiment, which is designed to decouple the effect of humidity and light on perovskite degradation, we investigate the shelf-lifetime of CH3NH3PbI3 films in the dark and under illumination under high humidity conditions (Rel. H. > 70%). We note minor degradation in perovskite films stored in a humid dark environment whereas upon exposure to light, the films undergo drastic degradation, primarily owing to the reactive TiO2/perovskite interface and also the surface defects of TiO2. To enhance its air-stability, we incorporate CH3NH3PbI3 perovskite in a polymer (poly-vinylpyrrolidone, PVP) matrix which retained its optical and structural characteristics in the dark for ∼2000 h and ∼800 h in room light soaking, significantly higher than a pristine perovskite film, which degraded completely in 600 h in the dark and in less than 100 h when exposed to light. We attribute the superior stability of PVP incorporated perovskite films to the improved structural stability of CH3NH3PbI3 and also to the improved TiO2/perovskite interface upon incorporating a polymer matrix. Charge injection from the polymer embedded perovskite films has also been confirmed by fabricating solar cells using them, thereby providing a promising future research pathway for stable and efficient perovskite solar cells

SnO2–TiO2 Hybrid Nanofibers for Efficient Dye-Sensitized Solar Cells

Pristine SnO2 nanostructures typically result in low open circuit voltage (VOC) <500 mV due to the lower Fermi energy (EF) when employed as a photoanode materials in dye sensitized solar cells (DSSCs). On the other hand, the most successful photoanode material, i.e., TiO2 nanoparticle although provides a high VOC ⩾ 800 mV result in poor charge collection owing to their inferior electron mobility (μn). Herein, we employ nanofiber–nanoparticle composite of SnO2–TiO2 which showed similar VOC and short circuit current density (JSC) to a reference TiO2 based DSSCs. The nanocomposite developed here involves multi-porous SnO2 nanofibers characterized by a lower EF; however, with higher μn and TiO2 nanoparticles of higher EF and lower μn. The TiO2 particles in the pores of SnO2 nanofibers were developed by TiCl4 treatment, whose concentration is optimized for the saturated JSC and VOC. The best performing DSSCs fabricated using the composite electrodes deliver power conversion efficiency (PCE) of ≈7.9% (VOC ≈ 717 mV; JSC ≈ 21 mA cm−2), which is significantly higher than pure SnO2 photoanode with PCE ≈ 3.0% (JSC ≈ 14.0 mA cm−2 and VOC ≈ 481 mV) at similar experimental conditions

Development of New Monitoring System for Field Information of Real Time Power Consumption in Malaysia

Abstract: World is currently suffering from energy crises affecting even developed countries like USA and European countries. Rapid increase in electrical energy demand for a developing country like Malaysia is a constant threat for &quot;Energy Plan 2020&quot;. This paper introduces a new energy strategy for electrical vendors in Malaysia, a way out to this growing challenge, an energy management system. This system consist of a new energy calculation algorithm, offering electricity packages with a intelligent monitoring system for daily power consumption connected to base-station via GSM network. A smart meter is back bone for this algorithm generating automatic bill, providing a necessary help to decrease peak curve line for electric consumption. Our proposed solution will be a very easy and updated system for monitoring companies and also offering the users,( mostly on industrial level which is almost 37.7% of total power consumption) a friendly packages surely resulting in change in energy sector

Optimizing Performance and Operational Stability of CsPbI3 Quantum-Dot-Based Light-Emitting Diodes by Interface Engineering

Perovskite light-emitting diodes (PeLEDs) have emerged as a promising candidate for next-generation display technology and lighting applications owing to their high current efficiency, low operating voltage, narrow spectral emission, and tunable emission color. Keys to achieving efficient PeLEDs are, besides an emitter layer with high optical quality, a negligible charge injection barrier between charge injecting layers (CILs) and an optimized thickness of these CILs for a controlled flow of charge carriers through the device. In this study, we systematically optimized hole transport layers and electron transport layers (ETLs) in PeLEDs employing CsPbI3 quantum dots as an emitter layer. We also investigated two bilayer cathodes (Liq/Ag and LiF/Al) with the various ETLs employed in our study and observed that 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T) as an ETL improves the band alignment, leading to better electron injection. The improved electron/hole current balance results in ∼63% higher external quantum efficiency (EQE) in PO-T2T-based devices compared to PeLEDs employing other ETLs. In addition, we tracked the operational stability of the different devices observing a correlation with the EQE, where samples with higher EQE (PO-T2T-based devices) also present the highest stable operation at elevated current densities

Tuning optical/electrical properties of 2D/3D perovskite by the inclusion of aromatic cation

The employment of bulky aliphatic cations in the manufacture of moisture-stable materials has triggered the development and application of 2D/3D perovskites as sensitizers in moisture-stable solar cells. Although it is true that the moisture stability increases, it is also true that the photovoltaic performance of 2D/3D PVK materials is severely limited owing to quantum and dielectric confinement effects. Accordingly, it is necessary the synthesis and deep optical characterization of materials with an adequate management of dielectric contrast between the layers. Here, we demonstrate the successful tuning of dielectric confinement by the inclusion of a conjugated molecule, as a bulky cation, in the fabrication of the 2D/3D PVK material (C6H5NH3)2(CH3NH3)n1PbnI3n+1, where n = 3 or 5. The absence of excitonic states related to n Z 1 at room temperature, as well as the very low concentration of excitons after 1 ps of excitation of samples in which n Z 3, provide strong evidence of an excellent ability to dissociate excitons into free charge carriers. As consequence films with low n, presenting higher stability than standard 3D perovskites, improved significantly their performance, showing one of the highest short circuit current density (Jsc E 13.8) obtained to date for perovskite materials within the 2D limit (n o 10)

Advances in solution-processed near-infrared light-emitting diodes

Near-infrared light-emitting diodes based on solution-processed semiconductors, such as organics, halide perovskites and colloidal quantum dots, have emerged as a viable technological platform for biomedical applications, night vision, surveillance and optical communications. The recently gained increased understanding of the relationship between materials structure and photophysical properties has enabled the design of efficient emitters leading to devices with external quantum efficiencies exceeding 20%. Despite considerable strides made, challenges remain in achieving high radiance, reducing efficiency roll-off and extending operating lifetime. This Review summarizes recent advances on emissive materials synthetic methods and device key attributes that collectively contribute to improved performance of the fabricated light-emitting devices