Lead-based halide perovskites have been widely used asefficientenergy materials due to their superior optoelectronic properties andmixed electronic-ionic conductivity. However, lead toxicityhas been one of the key challenges for commercialization. RecentlyCs(2)AgBiBr(6), a lead-free double perovskite, hasgarnered significant interest due to its exceptional stability, nontoxicnature, and promising optoelectronic properties. But because of thelow electronic and ionic conductivity of bismuth-based double perovskites,there is a challenge for their use in energy storage applications.To resolve this issue, we have incorporated carbon black and a conductingpolymer poly(2,3-dihydrothieno-1,4-dioxin)-poly (styrene sulfonate)(PEDOT:PSS) as electronic and ionic conductivity agents respectivelyinto the Cs2AgBiBr6 porous electrode. This ternarycomposite exhibits over 40% enhancement in specific capacitance aswell as specific energy density compared with a binary composite ofcarbon black with a perovskite electrode. There is no significantchange in the power density. However, only PEDOT:PSS as charge transportingmaterials in perovskite matrix results in lower energy density andpower density despite lower charge transfer resistance (R (ct)) at the electrode/electrolyte interface and higherdc ionic conductivity compared to perovskite/carbon composite electrodes.From the electrochemical impedance spectroscopy analysis, it is evidentthat balanced ionic and electronic conductivities are necessary toachieve optimal performance in lead-free perovskite-based supercapacitors.We also fabricated a solid-state symmetric supercapacitor using aquasi-solid-state gel electrolyte.

The Cover Feature illustrates empowering smart technologies: Halide perovskite photo-electrodes pave the way for off-grid energy storage in IoT and beyond. More information can be found in the Research Article by R. Kumar, M. Bag and co-workers.

Tuning the morphology of 2D/3D heterostructure perovskite electrode to boost the conversion efficiency and stability of photo-rechargeable ion capacitors for the application in remote sensors for smart cities and IoTs.

The right balance between photo-absorption and electronic-ionic conductivity is needed for photo-rechargeable bifunctional devices for off-grid energy applications. Recently halide perovskites have been utilized for photo-rechargeable supercapacitors, but the mechanism of photo-capacitance enhancement is not known. Herein, we have fabricated mixed halide perovskites-based photo-rechargeable supercapacitors in two ways and examined the energy harvesting and storage capabilities of these devices. The porous electrode prepared from the mixed halide perovskites (CH3NH3PbBr2I) shows photo-capacitance enhancement up to 15 F/g, while the electrode prepared from the blend of CH3NH3PbBr3 and CH3NH3PbI3 (2 : 1 by molar ratio) shows the photo-capacitance diminution up to 12 F/g. Despite higher specific capacitance (& SIM;38 F/g in dark) in blend perovskites due to increased ion diffusion, the photo-generated charge trapping at nanoscale phase segregation is responsible for the diminution in photo-capacitance of these bifunctional devices, while a uniform mixing of halide ions in mixed halide perovskites nanocrystals leads to increased photo-capacitance.

Current approaches for off-grid power separate the processes for energy conversion from energy storage. With the right balance between the electronic and ionic conductivity and a semiconductor that can absorb light in the solar spectrum, we can combine energy harvesting with storage into a single photoelectrochemical energy storage device. We report here such a device, a halide perovskite-based photorechargeable supercapacitor. This device can be charged with an energy density of 30.71 W h kg-1 and a power density of 1875 W kg-1. By taking advantage of the semiconducting and ionic properties of halide perovskites, we report a method for fabricating efficient photorechargeable supercapacitors having a photocharging conversion efficiency (η) of ∼0.02% and a photoenergy density of ∼160 mW h kg-1 under a 20 mW cm-2 intensity white light source. Halide perovskites have a high absorption coefficient, large carrier diffusion length, and high ionic conductivity, while the electronic conductivity is improved significantly by mixing carbon black in porous perovskite electrodes to achieve efficient photorechargeable supercapacitors. We also report a detailed analysis of the photoelectrode to understand the working principles, stability, limitations, and prospects of halide perovskite-based photorechargeable supercapacitors.