Quantum efficiency evolution in a hole-injection layer inserted within a polymer light-emitting diode

Based on a time-dependent theoretical description of electronic transitions, the evolution of quantum efficiency is explored and illustrated in detail. When a hole-injection layer is embedded inside the sandwich structure of a polymer light-emitting diode (PLED), the ultrafast process of a collision between an injected positive polaron and triplet exciton not only induces the triplet exciton to be an emissive carrier, but also immediately improves the quantum efficiency to 37% at the beginning of the relaxation. Considering the radiative decay of a singlet exciton, this ultrafast process also improves the quantum efficiency, but limits it to 25% within 1.0 ns. These two different emissive processes comprise the whole evolution of quantum efficiency for the new PLED, and both of them improve the quantum efficiency to 62.5%, which is consistent with the experimental result of 60%.