Constructing a dual gradient structure of energy level gradient and concentration gradient to significantly improve the high-temperature energy storage performance of all organic composite dielectrics†

The severe electrical conduction loss at elevated temperature is the initial factor for the degradation of energy storage performance of polymer dielectric films, thus it urgently needs to develop highly heat-resistant polymer capacitive films for meeting the advancing electrical and electronic applications. For reducing conduction loss and improving the high-temperature energy storage performance of dielectrics, the current approaches are focusing on preventing carriers mobility at elevated temperature and high electric field. In this study, the molecular semiconductor ITIC (ITIC is an organic molecular semiconductor 2,2′-[[6,6,12,12-Tetrakis(4-hexylphenyl)-6,12-dihydrodithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene-2,8-diyl]bis [methylidyne(3-oxo-1H-indene-2,1(3H)-diylidene)]]bis[propanedinitrile] abbreviation) with high electron affinity was filled into the blends of polyether imide (PEI) and polyethersulfone (PESU). The energy level gradient was constructed due to the different energy bandgap structures among ITIC, PESU and PEI. In addition, the concentration structure gradient was constructed due to the concentration of ITIC which varies along the thickness direction. The results demonstrate that the dual gradients of energy level and concentration can effectively inhibit carrier migration and lower conduction loss, thus significantly improving the electric breakdown strength and energy storage performance at high temperature. The energy storage densities (Ue) of 5.14 J/cm3 and 3.6 J/cm3 at 150 °C and 200 °C, respectively were achieved in PEI/PESU blends with 9 layers of ITIC gradient and 0.25 % ITIC in the outer layer. This study puts forward a novel structural design combining the energy levels gradient with concentration gradient to optimise the high-temperature energy storage properties of all-organic dielectric films.