Memory effect from charge trapping in layered organic structures

We demonstrate organic light emitting devices (OLEDs) with a charge trap layer that show memory behavior. These OLEDs demonstrate that organic heterojunction structures can controllably trap and release electronic charges. The trap layer is either 5-nm-thick clustered silver islands, or a 10-nm-thick organic laser dye DCM2 ([2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizin-9-yl)-ethenyl]-4H-pyran-4-ylidene] propane-dinitrile) doped into TPD (N,N-'-diphenyl-N,N-'-bis(3-methylphenyl)-1,1(')-biphenyl-4,4(')-diamine). Predictions of the energy band structure indicate that both DCM2 sites and the metal islands can trap charge, consistent with the measured current-voltage characteristics. Trap sites are charged by applying reverse bias over the OLEDs. For devices with DCM2 traps we observe quenching of DCM2 photoluminescence upon charging, which allows us to quantify the charged trap density as approximately 10% of the trap sites or 10(18) cm(-3). From time resolved measurements we observe that the charge retention time exceeds 2 h. (C) 2004 American Institute of Physics.