Perovskite light-emitting diodes have almost reached the threshold for potential commercialization within a few years of research. However, there are still some unsolved puzzles such as large ideality factor and the presence of large negative capacitance especially at the low-frequency regime yet to be addressed. Here, we have fabricated a methylammonium lead tri-bromide perovskite n–i–p structure for light-emitting diodes from a smooth and textured emissive layer and demonstrated for the first time that these two factors are strongly dependent on the perovskite film morphology. Bias-dependent capacitance measurement also reveals the transition between negative to positive capacitance in textured films at the low-frequency regime. We have observed an anomalous capacitive behavior at the mid-frequency regime in smooth perovskite films but not in textured films. The relatively large ideality factor and anomalous capacitive behavior observed in perovskite light-emitting diodes are due to the presence of strong coupling between ions and electrons near the electrode interface. Therefore, the ideality factor and anomalous capacitance at the mid-frequency regime can be decreased by minimizing electronic–ionic coupling in textured perovskite films, while light outcoupling can be improved significantly.

Room temperature broadband photoresponse through a single device is still the precedency of the scientific community. Many techniques, such as extensive nanoscale patterning, heterostructure patterning/growth, and field-induced band gap tuning, have been employed in this direction. However, the room temperature photoresponse of existing photodetectors is limited in a single region of the electromagnetic spectrum. We report room temperature broadband photoresponse from the visible to mid-infrared (MIR) region in a nanolayered black arsenic−silicon (bAs−Si) lateral heterojunction-based photodetector. Such a broad spectral range has been facilitated because of the suitable intrinsic band gap of bAs and of Si. This photodetector is fabricated using the mechanical exfoliation of bAs on the silicon-on-insulator (SOI) substrate. The fabricated device shows high photoresponsivities, in the visible to MIR (405 nm to 4 μm) region, which stems from the high absorptivity of bAs and good optical coupling capability of the SOI substrate. The maximum photoresponsivities are obtained as 72.15, 930.49, and 75.2 A/W for the wavelengths 785 nm, 1.05, and 3 μm, respectively. The corresponding maximum detectivities are 3.2 × 10 9 , 4.17 × 10 10 , and 3.37 × 10 9 Jones, respectively. This photodetector is capable of sensing a weak optical signal in terms of noise equivalent power from pico to femto W/ Hz 1/2 . Along with this, it has also been observed that this photodetector is slightly sensitive to the polarized incident radiation owing to the anisotropic crystal structure of bAs. Therefore, we envisage the integration of bAs with silicon to offer an enforceable pathway toward the realization of SOI technology for a wide range, including MIR, of optoelectronics.

Inorganic-organic hybrid perovskite materials have been a topic of interest for last few years due to their superior optoelectronic properties. However optical properties of perovskite materials are strongly dependent on...

Remarkable improvement in the perovskite solar cell efficiency from 3.8% in 2009 to 25.5% today has not been a cakewalk. The credit goes to various device fabrication and designing techniques employed by the researchers worldwide. Even after tremendous research in the field, phenomena such as ion migration, phase segregation, and spectral instability are not clearly understood to date. One of the widely used techniques for the mitigation of ion migration is to reduce the defect density by fabricating the high-quality perovskite thin films. Therefore, understanding and controlling the perovskite crystallization and growth have become inevitably crucial. Some of the latest methods attracting attention are controlling perovskite film morphology by modulating the coating substrate temperature, antisolvent treatment, and solvent engineering. Here, the latest techniques of morphology optimization are discussed, focusing on the process of nucleation and growth. It can be noted that during the process of nucleation, the supersaturation stage can be induced faster by modifying the chemical potential of the system. The tailoring of Gibbs free energy and, hence, the chemical potential using the highly utilized techniques is summarized in this minireview. The thermodynamics of the crystal growth, design, and orientation by changing several parameters is highlighted.

Hybrid organic−inorganic halide perovskite-based light-emitting diodes (PeLEDs) have attracted tremendous interest because of their higher external quantum efficiency and low production cost. Most of the high efficiency PeLEDs utilize a p−i−n structure geometry, which require a sufficiently low work function top metal electrodes for better charge injection. Also, PeLEDs can be fabricated at low temperature except the top metal electrodes. In conventional PeLEDs, metal electrodes are deposited by thermal deposition, which greatly reduces the production yield and enhances the complexity and production cost. Here, we have demonstrated a facile lowtemperature and vacuum-free deposition method for conformal coating of the low melting point alloy as the top cathode electrode which also facilitates efficient charge extraction. Ultraviolet photoelectron spectroscopy measurement has been performed to estimate the work function of this low melting point alloy. To our surprise, a sufficiently low work function (∼3.01 eV) has been observed despite all the constituents having a work function around 4.0 eV. XPS measurement confirms the presence of a metal hydroxide at the electrode interface which is responsible for achieving such a low work function due to surface polarization. These devices are relatively more stable compared to other low work function metal electrode-based PeLEDs.

No abstract

Organometal halide perovskites (MHPs) are widely used in energy harvesting as well as energy storage applications due to their superior optoelectronic properties. However, structural, optical, and electronic properties of these materials are strongly dependent on the halide substitution. So far methylammonium lead tri‐bromide‐perovskite‐based supercapacitors have shown an energy density in the range of 10–15 Wh kg−1. Therefore, further optimization is needed to improve the energy storage efficiency in halide perovskite‐based supercapacitors. It has been observed that the charge storage capacity increases with the increasing ionic conductivity in the perovskite active layer. Herein, a series of porous electrodes are prepared to optimize ionic conductivity by mixing powders of different halide‐based perovskite single crystals for supercapacitor application. It has been demonstrated that maximum efficiency is achieved for a specific bromide composition to iodide ratio with an energy density of ≈22 Wh kg−1 and a power density of 600 W kg−1. The ionic conductivity is improved at least by two orders to 3.2 × 10−13 m2 s−1 in the mixed halide sample than pure halide perovskites, while charge transfer resistance is decreased to 40.5 Ω cm−2. However, overall device stability and Coulombic efficiency decrease with the increasing iodide content.

Ion migration in hybrid halide perovskites is ubiquitous in all conditions. However, ionic conductivity can be manipulated by changing the material composition, operating temperature, light illumination, applied bias as well...