Record Energy Storage Performance Metrics in Ferroelectric Hafnia‐Based Films through Heterostructure Design

ABSTRACT Capacitive energy storage is part of a promising energy harvesting and storage solution to power Internet of Things (IoT) sensors, overcoming the critical limitations of conventional supercapacitors and micro‐batteries. Moreover, achieving high recoverable energy storage density ( ESD ) and high efficiency ( η ) simultaneously is a key goal in energy storage, often requiring hybrid systems (e.g., combining batteries and supercapacitors) to balance the trade‐offs. Here, we demonstrate a ultra‐thin film capacitor with unprecedented high ESD that can be efficiently released at low operating voltage. This is achieved by using a novel heterostructure design combining ferroelectric La‐doped HfO 2 and a ferroelectric perovskite that is a relaxor induced by polar nanoregions, which enables a low hysteresis loss in the capacitor, thereby leading to an improved η . Additionally, the relaxor ferroelectric layer thickness was optimized to give an optimum voltage drop to allow high maximum polarization and low remnant polarization, the former to allow an ESD of over 50 J/cm 3 , and the latter to allow ŋ to be maximized at ∼95%. Therefore, our fluorite/perovskite heterostructure design and unique materials strategy have together provided a novel way to achieve unprecedented dielectric energy storage properties, proving a new route to electrostatic energy storage for autonomous IoT sensors.