Magneto-conductance characteristics of trapped triplet–polaron and triplet–trapped polaron interactions in anthracene-based organic light emitting diodes

Abstract

The effects of a magnetic field on the dissociation of triplet excitons by free charges (TCI) are well understood. However, the magneto-conductance (MC) characteristics of trapped triplet–polaron interactions (T_tPI) and triplet–trapped polaron interactions (TP_tI) within organic light emitting diodes (OLEDs) are not well understood. We have studied these interactions in an anthracene-based OLED. The electroluminescence spectra, current–voltage characteristics and magneto-electroluminescence indicated that the anthracene layer contained many defects that could trap either triplet excitons or polarons, which led to TP_tI and T_tPI. The MC curves at low temperature exhibited a complex line shape, which indicated that intersystem crossing, TP_tI, T_tPI, and TCI occurred simultaneously in the device. The individual MC characteristics of TP_tI and T_tPI were extracted from temperature dependant MC curves by fitting them to three empirical Lorentzian functions and one non-Lorentzian function. The MC of TP_tI exhibited a negative sign, while that of T_tPI exhibited a positive one, with characteristic magnetic fields (B₀) of ∼10.5 and ∼15 mT, respectively. Both processes were prominent below 150 K and weakened with increasing temperature. TP_tI was neglected above 200 K, while T_tPI was observed even at ambient temperature. These results add significant insight into the magnetic field effects on triplet–polaron interactions.