Polymer/molecular semiconductor all-organic composites for high-temperature dielectric energy storage

Chao Yuan,Jiajie Liang,Simin Peng,Rong Zeng,Bo Zhang,Jun Hu,Yao Zhou,Yujie Zhu,Mingcong Yang,Qi Li,Shaojie Wang,Yushu Li,Sang Cheng,Jinliang He

doi:10.1038/s41467-020-17760-x

Abstract

Dielectric polymers for electrostatic energy storage suffer from low energy density and poor efficiency at elevated temperatures, which constrains their use in the harsh-environment electronic devices, circuits, and systems. Although incorporating insulating, inorganic nanostructures into dielectric polymers promotes the temperature capability, scalable fabrication of high-quality nanocomposite films remains a formidable challenge. Here, we report an all-organic composite comprising dielectric polymers blended with high-electron-affinity molecular semiconductors that exhibits concurrent high energy density (3.0 J cm−3) and high discharge efficiency (90%) up to 200 °C, far outperforming the existing dielectric polymers and polymer nanocomposites. We demonstrate that molecular semiconductors immobilize free electrons via strong electrostatic attraction and impede electric charge injection and transport in dielectric polymers, which leads to the substantial performance improvements. The all-organic composites can be fabricated into large-area and high-quality films with uniform dielectric and capacitive performance, which is crucially important for their successful commercialization and practical application in high-temperature electronics and energy storage devices.

Highlights

Dielectric polymers for electrostatic energy storage suffer from low energy density and poor efficiency at elevated temperatures, which constrains their use in the harsh-environment electronic devices, circuits, and systems
The thermally stimulated depolarization current (TSDC) measurement confirms that blending the molecular semiconductors into a typical heat-resistant dielectric polymer (PEI, i.e., polyetherimide) brings extra carrier trap sites in the resultant all-organic composites, with the trap energy level estimated to be around 1.5 eV (Supplementary Fig. 5)
We found that the all-organic composites exhibited significantly higher electrical resistivity with respect to the pristine polymer at the optimal compositions (0.25, 0.50 and 0.75 vol.% of the semiconductors for the PEI/ITIC, PEI/PCBM and PEI/DPDI composites, respectively) (Supplementary Figs. 6 and 7)

Summary

Introduction

Dielectric polymers for electrostatic energy storage suffer from low energy density and poor efficiency at elevated temperatures, which constrains their use in the harsh-environment electronic devices, circuits, and systems. We demonstrate that molecular semiconductors immobilize free electrons via strong electrostatic attraction and impede electric charge injection and transport in dielectric polymers, which leads to the substantial performance improvements. We depart from the previous approaches and show that a scalable all-organic composite comprising dielectric polymers blended with a low concentration (0.25–0.75 vol.%) of high-electron-affinity molecular semiconductors can attain record energy storage performance up to 200 °C. This would give rise to a large trap energy level (Φe = EAms − EAp, e.g., 1.5 eV) for the captured electrons to escape from the trap sites (Fig. 1b) This is fundamentally different from the insulating nanostructures in the previous high-temperature polymer nanocomposites, which introduce trap sites mainly through modification of the polymer chain conformation and arrangement in the particle/matrix interface (the Φe is usually below 1.0 eV) (Fig. 1c)[14,20,21]. We hypothesize that the deep traps introduced by the molecular semiconductors would firmly immobilize the free electrons in the polymer even under high temperature and high electric field conditions if the molecular semiconductors are thermally stable and their concentrations are well below the percolation threshold

Methods

Results

Conclusion