Self-enhancement in the electroluminescence of a near-infrared ionic dye

This letter reports self-enhancement behavior observed in the near-infrared electroluminescence (EL) of an ionic dye, 2-[6-(4-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl]-3-methylbenzothiazolium perchlorate doped in poly(N-vinylcarbazole). The EL intensity measured under a constant current, and therefore, the external EL quantum efficiency (phi(ex)), increases with time both when the EL is generated continuously in a constant current mode and kept in a no-bias field, whereas it decreases in a reverse-bias field. With an enhancement factor of about 80 under a constant current of 0.1 mA/cm2, phi(ex) reaches the 1% photons/electron level. I conclude that the behavior originates from the enhanced electron and hole injection caused by the alignment of the doped ionic dye molecules along the bias field. (C) 2000 American Institute of Physics. [S0003-6951(00)01612-0].