High-Performance CeO2-Doped SrTiO3 Nanocomposite Films for Electrostatic Energy Storage and Integrated Optical Transparency.

This study demonstrates the design and realization of high-performance, transparent electrostatic energy storage film capacitors by integrating optical functionalities via a nanostructural engineering approach. A series of (1 - x)SrTiO3-xCeO2 [(1 - x)STO-xC, 0.0 ≤ x ≤ 0.5] films were grown on highly transparent (La0.03Ba0.97)SnO3 buffer electrode layers using pulsed laser deposition. The incorporation of CeO2 as a heterogeneous second phase generates lattice-mismatch-associated interfacial strain and structural heterogeneity, thereby transforming the nearly linear dielectric response of STO into a slim nonlinear polarization response with enhanced maximum polarization and low remanent polarization. The (1 - x)STO-xC films with x = 0.4 and 0.5 exhibit exceptional electrostatic energy storage performance, attaining a high recoverable energy density of up to 50 ± 3 J/cm3 and an ultrahigh efficiency of ∼90%. These films simultaneously maintain a high optical transmittance of ∼75% across the visible to near-infrared spectrum with a tunable optical bandgap. These films demonstrate robust frequency reliability from 20 Hz to 5 kHz and thermal stability from 25 to 120 °C. Notably, these lead-free (1 - x)STO-xC films comprise merely four elements (Sr, Ti, O, and Ce). This work establishes a viable strategy for fabricating a simplified-composition, multifunctional film that simultaneously delivers superior energy storage capability and high optical transparency, advancing their integration into next-generation transparent optoelectronic systems.