Largely improved dielectric properties of polyimide composites by tuning content and formation of CsPbBr3 nanocrystals

Highlights

• Novel perovskite (CsPbBr₃)/polyimide composites were successfully prepared via an in-situ polymerization from CsPbBr₃ precursor in polyamic acid, followed by thermal imidization.

• The dielectric properties of polyimide composites were controlled by adjusting the content of CsPbBr₃ nanocrystals.

• The obtained CsPbBr₃/PI composites possess a high dielectric constant of up to 25.5 but also exhibit low dielectric loss below 0.25.

• The CsPbBr₃/PI composites possess a high dielectric constant of up to 25.5 and dielectric loss below 0.25，and excellent thermal properties and good mechanical properties.

Abstract

High dielectric constant polymer composites have considerable potentials in energy storage and dielectric applications because of simple fabrication process, facile processability, light-weight, excellent thermal stability and mechanical properties. Perovskite (CsPbBr₃)/polyimide (PI) composites were successfully prepared via an in-situ polymerization from CsPbBr₃ precursor in polyamic acid, followed by thermal imidization. The dielectric properties of polyimide composites were controlled by adjusting the content of CsPbBr₃ nanocrystals. The obtained CsPbBr₃/PI composites not only possess a high dielectric constant of up to 25.5 but also exhibit low dielectric loss below 0.25. The maximal discharging energy density reached up to 3.10 J cm⁻³ with 10% CsPbBr_3, which is almost 3 times greater than pure PI under the same conditions. In addtiton, outstanding thermal properties of 5% decomposition temperature beyond 530 °C and good mechanical properties. The CsPbBr₃/PI composites can be prepared facilely and rapidly on a large scale, which will be a outstanding dielectric material for high temperature polymer film capacitors.

Introduction

High dielectric constant (high-k) materials with excellent thermal and mechanical properties are highly desirable in recent years for their advanced applications in the modern electronics and electrical industry[[1], [2], [3], [4], [5]], such as electrical stress control[[6], [7], [8]], polymer film capacitors[[9], [10]], dielectric elastomer actuators[[11], [12], [13]] and transistors[14]. Inorganic materials (e.g., ceramics) usually exhibit high-k, high stiffness and excellent thermal stability, but their high density, brittleness and challenging processing conditions impede their use for flexible and lightweight applications. Polymer dielectric materials have advantages of high breakdown strength, low dielectric loss, good mechanical flexibility, light weight and easy processabilities [15,16]. However, most polymers generally exhibit dielectric constant of 2–5[17], which are too low to be used for high-k applications. A kind of polymer-metal complexes reported recently well combines high-k and low dielectric loss[18,19]. However, their preparation often relies on complicated and time-consuming routes, which tremendously restrict their further economical and large-scale applications.

Rational composite design of polymers and inorganic materials can maintain the low-temperature processability, mechanical properties and high breakdown strength of polymers [20,21] and introduce high-k performance of inorganic materials [[22], [23], [24]]. The major challenges for excellent high-k polymer composites involve uniform dispersion of inorganic fillers into polymer matrix and good interfacial compatibility. This is because poor compatibility and uneven dispersion of inorganic filler in the polymer matrix result in low breakdown strength and high energy loss[25,26]. Usually inorganic fillers were directly loaded into polymers to fabricate composites with the aid of mechanical force. This frequently-used strategy is convenient, low cost and easy for mass production. However, it cannot guarantee the homogeneous dispersion of target fillers, particularly for the fillers in nanoscale, i.e., nanomaterials. Semiconductor nanomaterials fillers are good candidates for high-performance dielectric composites even at a low concentration[22], but they usually tend to agglomerate in the continuous matrix inhomogeneously. A conventionally improved strategy is to first pretreat nanomaterials with suitable surface properties and then directly mix them with target polymers for more homogeneous dispersion.

Different from simply blend (modified) nanomaterials with final polymers, herein we present an unconventional composite strategy for a kind of high-k polymer composites with low dielectric loss, outstanding thermal properties and good mechanical properties by a novel in-situ synthesis strategy of using perovskite nanomaterial precursors and polyimide (PI) polymer precursors [[27], [28]]^. They both can be well dissolved in an identical solvent to obtain a true solution for further preparation of liquid membrane by casting. A solidified membrane with highly homogeneous precursors is easy to be obtained by the removal of solvent through simply preheating. Further in-situ thermal imidization of precursor membrane leads to final formation of high-k polymer composite films.