Significantly enhanced energy storage density and efficiency in flexible Bi_3.15Nd_0.85Ti₃O₁₂ thin film via periodic dielectric layers

Flexible energy storage based on ferroelectric capacitors enjoys high power density and rapid respond time, but the polarization fatigue problems limit its long-term reliability. Bi3.15Nd0.85Ti3O12 (BNT) is a lead-free ferroelectric material with fatigue-free properties, which is promising for applications in long-term ferroelectric devices. Nevertheless, the applications of BNT thin films for energy storage are restricted by their poor energy efficiency and low energy density. In this work, flexible BNT thin films with different numbers of SrTiO3 (STO) insert layers are fabricated on flexible mica substrates by an exquisitely designed dual-target pulsed laser deposition process, and the energy storage performances are effectively optimized via interface engineering. By inserting periodic STO dielectric layers with repetition periods of 100, the energy storage density ( Wrec) and efficiency ( η) are improved to ∼24.26 J cm−3 and ∼71.93%, which are, respectively, increased to 287% and 132% compared with the pure phase BNT thin film. Importantly, the improved Wrec and η can be well maintained under large bending deformation (bending radius as small as r = 4 mm) and within a wide temperature range (25–175 °C), suggesting its good stability and reliability. These results show that the involvement of periodic dielectric layers in BNT thin films can significantly enhance energy storage density and efficiency and effectively promote its applications in future flexible energy storage devices.