  In this study, we develop a steady state and time-dependent exciton diffusion
model including singlet and triplet excitons coupled with a modified Poisson
and drift-diffusion solver to explain the mechanism of hyper triplet-triplet
fusion (TTF) organic light-emitting diodes (OLEDs). Using this modified
simulator, we demonstrate various characteristics of OLEDs, including the J-V
curve, internal quantum efficiency, transient spectrum, and electric profile.
This solver can also be used to explain the mechanism of hyper-TTF-OLEDs and
analyze the loss from different exciton mechanisms. Furthermore, we perform
additional optimization of hyper-TTF-OLEDs that increases the internal quantum
efficiency by approximately 33% (from 29% to 40%).
