Dye-doped molecular light-emitting diodes with enhanced performance

We present the first comprehensive study of the comparison between electroluminescence (EL) quantum efficiency and absolute photoluminescence (PL) quantum yield in various host-guest systems. We find that the maximum quantum yield of solid composite films primarily depends on the quantum yield of the guest molecule itself. In contrast, the maximum quantum efficiency of multilayered devices depends on both guests and hosts. Differences between the maximum quantum efficiency and quantum yield are discussed in terms of the carrier recombination process leading to the creation of the dopant exciton. We also find that in some cases doping prevents exciplex formation and leads to an increase in EL efficiency. This is attributed to rapid energy transfer form the host to the guest molecule followed by efficiency radiative decay.