Defect Engineering of Mott–Schottky Heterostructure for Flexible High-Performance Energy Storage

Nickel-based transition metal selenides are promising hybrid supercapacitor (HSC) cathodes owing to their high capacity yet suffer from structural degradation, poor conductivity, and sluggish charge transfer, limiting cycling stability and rate performance. Herein, this study employs a synergistic approach by engineering a built-in electric field (BIEF) and Se vacancies in the NiSe2@FeSe(VNSFS) Mott–Schottky heterojunction that enhances structural integrity during the intercalation/deintercalation of electrolyte ions, promotes faster ion diffusion kinetics, induces large electroactive sites, and reduces the activation energy barrier. In situ/ex situ analyses and galvanostatic intermittent titration technique confirm enhanced ion diffusion, while DRT analysis evidences improved charge transfer dynamics. Furthermore, a quasi-solid-state VNSFS//AC flexible HSC delivers a high energy density of 94.17 Wh kg–1, without compensating power density of 750 W kg–1, with prolonged stability of 50,000 cycles. The device advances sustainability by integrating a commercial solar module for energy harvesting and storage, enabling ∼2 min charging to power various electronic devices while supporting wireless charging and efficient AC-filtering. Thus, this work offers high-safety and flexible energy storage devices.