An unreported peak of the electroluminescence turn-on transience from OLEDs with electron or hole potential well

An unreported peak was discovered at the transient electroluminescence (TEL) rising edge from pure emission layer (EML) based OLEDs with an energy potential well for electron or hole charge carriers. A series of control experiments indicated that the formation mechanism of this peak is completely different from the already-reported peak originated from exciton interactions such as singlet-triplet and triplet-triplet annihilations. Herein, the peak at the TEL rising edge is generated by the radiative recombination of injected carriers with pre-stored charges in the energy potential well. Surprisingly, for the pure EML-based OLEDs with simultaneous electron and hole potential wells, the peak at the TEL rising edge disappeared, and contrarily, a super-high spike was observed at the TEL falling edge. Such an already-reported spike at the TEL falling edge was considered to only appear in doped-EML systems. This contradiction leads to the reconsideration for the formation mechanisms of the spike at the TEL falling edge. Accordingly, this work not only deepens the physical understanding of the unprecedented peak at the TEL rising edge and the already-reported spike at the TEL falling edge, but also reveals the effects of the energy potential well on the carrier recombination process in OLEDs.