On August 6th, Associate Professor Li Qi and Professor He Jinliang from EEA published a research thesis entitled "Polymer/ molecular semiconductor all-organic composites for high-temperature dielectric energy storage" in Nature Communications, which disclosed an all-organic composite film for high efficiency dielectric energy storage at 200掳C for the first time. The dielectric energy storage properties of these all-organic composite dielectric materials at 200掳C are not only much higher than those of the best high-temperature polymers and polymer nanocomposite dielectric materials, but also close to those of commercial polymer capacitor films at room temperature; it not only greatly improves the characteristics of high-temperature dielectric energy storage, but also realizes the preparation of thin films with large area and uniform performance, making it possible to realize the application of thin film capacitors in the harsh temperature environment at 200掳C.

Polymer thin film capacitors have the advantages of high dielectric strength, low energy loss and favourable self-recovery, and the share in the global market of industrial capacitors is higher than that of other types of capacitor products (Source: Paumanok Publications, Inc.). However, the insulation performance of polymer dielectric materials is extremely sensitive to temperature. At a high temperature in a high electric field, the leakage current increases exponentially and the discharge efficiency decreases sharply, resulting in overheating damage of capacitors. Existing mainstream commercial film capacitors only work below 105掳C, and the long-term working temperature is below 70掳C. On the other hand, with the increasing power of electronic devices, power and energy equipment and the continuous pursuit of miniaturized and compact power modules, the working temperature of electronic materials is required to increase rapidly, but the dielectric material of thin film capacitor has become the technical bottleneck for high temperature electronic devices and equipment.

This thesis takes a highly different technical route from the previous approach: the construction of deep charge traps in high-temperature polymers is realized by exploiting the strong electron-accepting ability of electron-accepting materials in organic photovoltaics. This organic molecular semiconductor electron acceptor material with extremely high electron affinity energy is widely used for efficient separation of excitons at heterojunction interfaces in organic photovoltaics. They can strongly bind free electrons through the extremely non-uniform distribution of 、electrostatic potential on their surfaces. All-organic composite high temperature dielectric materials were prepared by doping a very small amount of high electron affinity organic molecular semiconductors into heat-resistant polymers. The resistivity of these materials is more than two orders of magnitude higher than that of high-temperature polymers at 200掳C in a 200kV/mm electric field, and the energy density at 掳200C and a discharge efficiency of more than 90% is 2.3 times that of the best high-temperature polymeric dielectric materials at present. In addition, the all-organic composite system solves the problems of uneven dispersion of high surface energy particles and the defects on the introduction interface in the traditional organic-inorganic composite system, and has significant advantages in film quality and large-scale preparation.

The first author of this thesis is Yuan Chao, a postdoctoral fellow of Tsinghua EEA, and the communication authors are Associate Professor Li Qi and Professor He Jinliang of EEA. The research was supported by the National Natural Science Foundation, Excellent Young Scientists Fund and the Innovative Research Group Project .