基于反向双异质结的高击穿场强反铁电-介电-反铁电复合薄膜的极化行为及储能性能研究

Dielectric capacitors are key devices for electrostatic energy storage, but their energy storage density is low. Based on the research of PbZrO3 antiferroelectrics with excellent performance, in this study, the dielectric insulation layer with wide band gap and high Fermi level has been introduced for construncting opposite double-heterojunction of the antiferroelectrics/dielectrics/antiferroelectrics composite thin films. The approache and mechanism which improve the energy storage performance of the composite thin films will be explored. The main contents of this study are given as follows: Firstly, the dielectric insulation thin layer is the carrier depletion layer due to carrier diffusion, leading to the formation of opposite double-heterojunction between the dielectric insulator layer and antiferroelectric layer. One of the heterojunction must be reverse-biased under electric field, resulting in the improvement of breakdown strength of composite films. In addition, the width of heterojunction and build-in electric field can be designed by regulating the energy band structures, meanwhile, the polarization behaviors of composite films can also be designed by the non-symmetry structure of antiferroelectric layer. Secondly, the dielectric insulator layer with smaller dielectric constant can endure and divide more external voltage, which is benefit to further improving the breakdown strength of composite films. Based on the design of the energy band structure and geometry structure through changing the thickness of films, the microstructures characterization, field-induced phase transition and polarization behaviors of the composite films have been systematically investigated in this project. The affecting factors and rules of the breakdown strength and the microscopic mechanism for the improvement of energy storage performance of composite films should be elucidated. The aim of this project is to optimize the energy storage performance of heterostructured-antiferroelectric based films capacitors, which provides the basis for developing energy storage dielectrics with excellent overall performance.

电介质电容器是重要的静电能存储器件，但其储能密度较低。本研究以性能优异的PbZrO3反铁电体为基础，通过引入宽禁带高费米能级介电绝缘层，构建含有反向双异质结的反铁电-介电-反铁电复合薄膜，探讨提高复合薄膜储能性能的途径与机制。主要思路如下：首先，介电绝缘薄层因载流子扩散而成为载流子耗尽层、并与反铁电层形成两个反向异质结，外场下某个异质结一定为反向偏置，从而提高复合薄膜的击穿场强；另外，通过能带结构设计结区宽度和自建电场，并借助反铁电层厚度非对称性设计复合薄膜的极化行为；其次，小介电常数的介电层具有分压作用，利于击穿场强的提高。本项目将在复合薄膜能带结构和几何结构（膜厚）设计的基础上，通过结构表征、场致相变和极化行为等研究，阐明复合薄膜击穿场强的影响因素及规律；揭示提高复合薄膜储能性能的微观机制；实现反铁电基异质结构复合薄膜电容器储能性能的优化；为开发具有优异综合性能的储能电介质提供依据。

电介质电容器是一类重要的静电能存储器件，在电气工程、电力电子、武器装备等诸多领域具有重要应用。锆酸铅（PbZrO3）反铁电薄膜因具有独特的场致相变行为而有望成为理想的储能介质材料，备受学者研究关注。本项目通过构筑锆酸铅反铁电层/介电绝缘层/锆酸铅反铁电层复合薄膜，利用介电绝缘层与反铁电锆酸铅层之间界面能带结构差异所形成的反向异质结构来提高复合薄膜的击穿场强，进而改善储能性能。通过调控复合薄膜的微观结构，几何结构等，综合调控复合薄膜的极化行为并揭示其储能性能提升机制。其中通过调控晶化温度，具有反向双异质结构的PZO/AO/PZO复合薄膜，其储能密度达32.6J/cm3，储能效率为88.1%。复合薄膜的击穿场强相比纯PZO薄膜提高了5倍左右，主要机制如下：选择AO膜层作为中间层，其与两侧PZO膜层在界面处均形成自建电场，一方面使得AO膜层中的载流子浓度大幅下降，甚至耗尽，大大提高了AO膜层的绝缘强度；另一方面具有反向双异质结构的PZO/AO/PZO复合薄膜，两个反向自建电场总有一个会部分抵消施加在薄膜上的外电场，进而提高了PZO/AO/PZO复合薄膜的击穿场强。其中需要特别指出的是本项目的“意外发现”，当介电绝缘层的几何厚度达到某一临界值时（不同介电绝缘材料的临界厚度各有不同），会诱导PZO反铁电膜层呈现铁电极化特征，场致相变行为消失。通过研究发现，介电绝缘层AO与反铁电膜层PZO之间的费米能级差驱动形成的自建电场，导致PZO反铁电膜层出现铁电自极化。此外，项目为了进一步验证构建反向双异质结构设计思想的普适性，借鉴柔性储能介质领域的前沿热点，项目又开展了有关PZO/AO复合薄膜柔性化制备技术及储能性能研究，解决了PZO/AO柔性复合薄膜的柔性化制备难点，其中AO/PZO/AO/PZO/AO柔性复合薄膜的储能密度达到30J/cm3，且效率保持在80%，同时展现出了优异的抗弯折疲劳性、温度稳定性以及循环寿命。项目研究为开发具有优异储能性能和使役性能的反铁电储能电介质提供实验依据和理论指导。

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