Tailoring by AgNPs of the Energetics of Charge Carriers in Electrically Insulating Polymers at the Electrode/Dielectric Contact

The ever increasing field of application of nanodielectrics in electrical insulations calls for description of the mechanisms underlying the performance of these systems and for identification of the signs exposing their aging under high electric fields. Such approach is of particular interest to electrically insulating polymers because their chemical defects are of deleterious nature for their electrical properties and can largely degrade their performance at high electric fields. Although these defects usually leave spectroscopic signatures in terms of characteristic luminescence peaks, it is nontrivial to assign, in an unambiguous way, the identified peaks to specific chemical groups or defects because of the low intensity of the signal with the main reason being that the insulating polymers are weakly emitting materials under electric field. In this work, we go beyond the conventional electroluminescence technique to record spectroscopic features of insulating polymers. By introducing a single plane of silver nanoparticles (AgNPs) at the near-surface of thin polypropylene films, the electroluminescent signal is strongly enhanced by surface plasmons processes. The presence of AgNPs leads not only to a much higher electroluminescence intensity but also to a strong decrease of the electric field threshold for detection of light emission and to a phase-stabilization of the recorded spectra, thus improving the assignment of the characteristic luminescence peaks. Besides, the performed analyses bring evidence on the capability of AgNPs to trap and eject charges, and on the possibility to adjust the energetics of charge carriers in electrically insulating polymers at the electrode/dielectric contact via AgNPs.