We have fabricated porous electrodes from three-dimensional (3D) bulk and 2D layered perovskite single crystals and demonstrated that the ion migration could play a significant role in determining the overall performance of the electrochemical supercapacitor. The areal capacitance (∼58 mF cm–2), specific capacitance (∼36.82 F g–1), and energy density (∼9 W h kg–1) calculated at a current density of 0.6 mA cm–2 are higher in 3D perovskite-based supercapacitors, while the maximum power density (∼400 W kg–1) is significantly higher in 2D perovskite-based supercapacitors due to faster intercalation/deintercalation of the electrolyte ions into the porous electrode. We have also estimated the amount of diffusion-controlled charge storage to that of electric double-layer capacitance and surface redox reaction (pseudo-) capacitance from the power law relation in both the samples.

Hybrid halide perovskites recently emerged as promising semiconductor materials for high-mobility field-effect transistors and detectors due to their unique optoelectronic properties. However, iontronics in these materials play a significant role in charge carrier dynamics. In addition, the impact of grain boundaries and trap density on the dielectric properties and the alternate current (AC) ionic conductivity has been one of the most debated topics. In this work, we have studied the electro-ionic dynamics in perovskite single crystals (SCs) using temperature-dependent impedance spectroscopy and the transient photovoltage (TPV) technique. The device capacitances are temperature-independent, revealing that the temperature is only accelerating the migration of ions (MA+ and Br–) but not increasing the number of ion migrations in single crystals. Moreover, the ions in perovskite single crystals are not trapped at the grain boundaries, and hence all of the ions participate in the conduction; this leads to a higher increase in conductivity resulting in the super-linear power law (SPL) region at a higher frequency. Furthermore, TPV measurements also confirmed the temperature independence recombination lifetime in these materials. The maximum values of responsivity (R), detectivity (D), and external quantum efficiency (EQE) are 12.35 mA/W, 5.89 × 109 Jones, and 38.8%, respectively. This work will be beneficial for understanding charge carrier dynamics in single-crystal field-effect transistors (FETs) and detectors.

2D-perovskites are generally more stable than 3D perovskites while charge transport in 2D-perovskites becomes inefficient.On the other hand, the instability of 3D perovskite films under heat, light and environmental conditions makes them inapplicable for practical purposes. Therefore, quasi-2D perovskites could be the optimum solution for stable yet highly efficient devices. Using the post-fabrication treatment method, we have converted methylammonium lead tribromide (MAPbBr3) 3D perovskite films into a quasi 2D-perovskite interfacial layer. In situ photoluminescence measurement during spin coating indicates a rapid conversion of 3D-perovskite into 2D-perovskites. The kinetics of oxygen and moisture diffusion, ion diffusion and electronic charge transport can be estimated from the time dependent PL measurements in the 3D and 2D/3D perovskite samples. 2D terminated perovskite samples show enhanced photoluminescence and improved stability in moisture and UV-irradiation. We also propose that a relatively wide bandgap of 2D-perovskite can give rise to a graded energy landscape at the interface for favorable charge separation. Simulation results reveal that the power conversion efficiency can be improved from 2.83% to 4.02% due to an increase in open-circuit voltage and fill factor in 2D/3D based MAPbBr3 solar cells without using any electron transport layer.

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 halide perovskites have become highly popular mixed electronic−ionic material over the past decade due to a wide range of applications in flexible optoelectronics especially for energy conversion and light-emitting devices. While ion migration in these materials is the main cause of device instability under heat and light, this property can make them ideal for energy storage applications such as Li-ion batteries, photorechargeable batteries, and supercapacitors. Herein, progress so far in the field of perovskite material-based electrochemical supercapacitors is summarized, unraveling charge storage mechanisms in these types of devices, as well as important perspectives for future development of the field. In these types of materials, the total charge/energy storage can be modulated by the induced field due to ion migration inside the bulk perovskite film. The electronic−ionic coupling in metal halide perovskite materials is crucial for the charge storage mechanism in perovskite-based energy storage devices. A general strategy is proposed to prepare the porous perovskite electrode from the powder of perovskite single crystals for high-performance perovskite supercapacitors. The modified power law equation for perovskite-based energy storage devices is proposed. In the end, the possibility of photorechargeable perovskite-based energy storage devices is also discussed.

Metal halide perovskites (MHPs) are the most exciting class of next generation energy storage materials owing to their high ionic as well as electronic conductivity. There has been tremendous progress in perovskite solar cells as well as perovskite light emitting diodes in last decade, however the use of halide perovskites is limited in energy storage application. Moreover, the device performance of MHP based supercapacitors is still inferior due to the lack of fundamental understanding of charge storage in perovskite supercapacitor. Here, we have fabricated methylammonium lead tri-bromide perovskite-based electrode by spin-coating as well as from the single crystal for electrolyte-based supercapacitors and demonstrated that the device performance strongly dependent on the electrode morphology. Our experimental results show that the modified electrode from the MHP single crystal has 500-time higher volumetric capacitance (∼ 429.1 F cm−3 @ 5 mV s−1) compared to the spin-coated thin-film based capacitors (∼ 0.8 F cm−3 @ 5 mV s−1) having same electrolyte and device structure. The modified electrode exhibits much higher ionic diffusion coefficient of 5.61 × 10−13 m2 s−1, and a very low charge transfer resistance (CTR) of ∼ 62.5 Ω cm−2 compared to thin film-based electrodes (Dion = 1.41 × 10−16 m2 s−1, CTR ∼ 4.4 kΩ cm−2) due to highly porous isotropic structure with high degree of micro-strain. Moreover, MHPs based supercapacitor exhibits a very quick energy deliver response time of 5 – 13 ms. We have got energy density ∼12.75 W h kg–1 at a power density of ∼225 W kg–1 which shows significant improvement in metal halide perovskite-based energy storage devices. We have found that the major contribution in powder electrode-based capacitor is diffusion limited capacitance while thin-film based devices show mainly electric double layer capacitance. Our modified powder electrode-based supercapacitors show significant improvement in terms of cyclic stability over 97% as well as coulombic efficiency over 91% after 1500 cycles of operation.

Ion migration in hybrid halide perovskites is ubiquitous in all conditions. However, the ionic conductivity can be manipulated by changing the material composition, operating temperature, light illumination, and applied bias as well as the nature of the interfaces of the devices. There have been various reports on electron ion coupling in hybrid perovskite semiconductors which gives rise to anomalous charge transport behavior in these devices under an applied bias. In this investigation, we have synthesized a mixture of 2D/3D perovskites by incorporating sulphur-doped graphene quantum dots (SGQDs) and demonstrated that the optical and electrical properties of the hybrid system can be tuned by controlling the ion conductivity through the active layer. It has been observed that the recombination resistance in undoped CH3NH3PbBr3 perovskites follows an anomalous behavior while the doped CH3NH3PbBr3 perovskite shows a monotonic increase with increasing applied bias due to reduced ionic conductivity. SGQDs at the grain boundaries of 2D/3D perovskites prohibit ion migration through the active layer, and therefore the electronic-ionic coupling is reduced. This results in increased recombination resistance with increasing applied bias.

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.