  Several models of the charge transfer exciton (CTE) have been proposed to
explain its dissociation at the donor-acceptor (DA) interface. However, the
underlying physics is still under debate. Here, we derive temperature
($T$)-dependent tight-binding model for an electron-hole pair at the DA
interface. The main finding is the existence of the localization-delocalization
transition at a critical $T$, which can explain the CTE dissociation. The
present study highlights the combined effect of entropy (finite-$T$) and
carrier delocalization in the CTE dissociation.
