Exciton Dissociation in Organic Light Emitting Diodes at the Donor-Acceptor Interface

Abstract

Experimental in situ photoluminescence and transient photovoltage results show that the interface formed by $N$, $N^{\prime }$-Bis(naphthalene-1-yl)-$N$, $N^{\prime }$-bis(phenyl) benzidine (NPB) and tris(8-hydroxyquinoline) aluminum (${\mathrm{Alq}}_3$) acts as an exciton dissociation site. Because of this dissociation effect, excitons formed in NPB at or within a diffusion length of the interface tend to dissociate before they radiatively decay to generate blue light. This suggests that the action of the “hole-blocking layer” used in indium tin oxide\NPB\hole-blocking $\mathrm{\text{layer}}\backslash {\mathrm{Alq}}_3\backslash \mathrm{\text{aluminium}}$ to promote blue light emission from the NPB is more “exciton dissociation inhibition” than “hole blocking.”