Hybrid perovskites have been widely used in solar cells and light-emitting diode applications due to superior optoelectronic properties. However, ion migration in these materials causes photo- and thermal instability. On the other hand, mixed electronic–ionic conduction could be advantageous in electrochemical energy storage applications. 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. The major difference is observed at a low-field regime, where ionic conductivity in 3D bulk perovskites is significantly higher than that in 2D-layered perovskites mainly due to strong electron–ion coupling. Therefore, in 3D perovskite-based supercapacitors, only 2% is diffusion-controlled charge storage compared to 40% in 2D samples at a low-field regime. With the increasing applied voltage, both capacitive and diffusion-controlled charge storage become comparable in both the samples. The 3D sample stability is ∼98%, while the 2D sample stability is almost 100% even after 1000 cycles of operation.

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.

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Mixed-cation mixed-halide perovskites have gained a lot of attention due to their superior device properties, optoelectronic properties, and improved structural stabilities over methyl ammonium lead trihalide-based devices. However, understanding the interfacial charge and ion transport kinetics remains elusive. In this article, we have synthesized (MA) x (FA) x−1 Pb(Br) 2+x (I) 1−x stoichiometric compositions by varying x between 0.2 and 1.0. We have chosen two compositions with x = 0.6 and 0.8 due to their similar morphologies and optical absorption properties. We have demonstrated that increasing MA + for x = 0.6−0.8 can reduce the ion migration by a factor of two while the activation energy for ion migration is increased from 0.36 eV to 0.47 eV. The ideality factor can be reduced upon increasing methylammonium bromide concentrations. We have measured ionic conductivity as a function of frequency to demonstrate that the interplay between A-site cation and X-site halide ion leads to opposite behavior in the low-frequency regime upon increasing bias voltage. This could be due to two competing processes; interfacial polarization and cation-halide hydrogen bonding in two samples. MA + and FA + migration lead to Jonscher's power law at the mid-frequency regime. High-frequency AC conductivity follows the nearly constant (dielectric) loss regime with exponent (slope) exceeding one due to the presence of multiple ions in the systems. This kind of superlinear power law behavior of AC ionic conductivity at operating temperature is reported for the first time in these perovskite materials.

Hybrid perovskite materials are mixed electronic–ionic conductors which enhance the complexity of conduction in these materials. Complete understanding of ionic conductivity along with electronic conductivity is crucial. Herein, we employed photoelectrochemical impedance spectroscopy on a perovskite/electrolyte interface-based device to investigate the role of an A-site cation and X-site halide ion in dictating the charge and ionic conductivity of the perovskite material. It was noted that ionic conductivity of the perovskite material can be tuned either by changing the A-site cation (MA+/FA+) or by changing the X-site halide ion (I–/Br–). Photoinduced ionic conductivity can be significantly different (opposite) in different cation perovskites or different halide-based perovskites. Therefore, mixed-cation perovskites can be utilized to reduce photoinduced ion conductivity. Furthermore, very fine tuning is also possible by modulating with the external applied bias. The influence of ion accumulation and migration on the charge storage and transport property of the device is analyzed using vacancy hopping and the jump relaxation model. Ionic conductivity spectra revealed Jonscher’s law dependence in the mid- and low-frequency range with a constant plateau at high frequencies. It can be concluded that the interplay of ion migration and accumulation decides the resulting conduction and storage property of the complete device. These perovskite/electrolyte-based devices can therefore be promising candidates for electrolyte-gated perovskite field-effect transistors where switchable ion conductivity can be achieved either by photoexcitation or external electric field.