Lead-free halide double perovskite (LFHDP) Cs ₂ AgBiBr ₆ has emerged as a promising alternative to traditional lead-based perovskites (LBPs), offering notable advantages in terms of chemical stability and non-toxicity.

The Cr–CsPbIBr ₂ device showed enhanced performance, with increased grain size, reduced energy band gap, and elevated efficiency from 9.64% to 12.06%.

PSCs rely on valence band (VB) and conduction band (CB) limits of perovskite films. Efficient electron injection requires a higher CB edge than the ETL's CB, while hole injection needs a lower VB edge than the HTL's VB in CsPbIBr₂.

Iron-doped tungsten disulfide (Fe-WS₂) nanoparticles were synthesized via a green method using neem leaf extract. X-ray diffraction (XRD) confirmed structural changes, with the formation of a hexagonal structure. The d-spacing is increased by Fe doping (6.05–6.08 Å). Fourier-transform infrared (FTIR) spectroscopy identified W–S and S–S bond vibrations, crucial for material integrity. The Brunauer–Emmett–Teller (BET) analysis confirmed the increased surface area and pore radius as a result of enhanced ions diffusion. The morphology study through Scanning Electron Microscopy (SEM) revealed enhanced porosity of Fe-WS₂, as evidenced by the more granular and disordered structure. UV-vis spectroscopy (UV-vis) showed a blue shift and an increased energy band gap from 2.48 eV to 2.64 eV, indicating improved optical properties. Methyl blue (MB) dye adsorption spectra showed that the Fe-WS₂ is porous, and as a result, more electrolyte adsorbs within the electrode. Cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) revealed enhanced specific capacitance and energy density. Electrochemical impedance spectroscopy (EIS) demonstrated a significant reduction in charge transfer resistance and a substantial increase in the ion diffusion coefficient. These findings underscore the potential of Fe-WS₂ for high-performance energy storage devices.