Charge-trapping effect of doped fluorescent dye on the electroluminescent processes and its performance in polymer light-emitting diodes

We have measured the temperature dependence of the steady-state current-voltage (I–V) characteristics and the transient electroluminescent (EL) characteristics in 4-(dicyanomethylene)-2-t-propyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) doped polyfluorene devices to study the charge-trapping effect of DCJTB fluorescent dye on luminescence processes and on device performance. Physical and chemical analyses prove that DCJTB molecules serve both as electron and hole traps, and the charge-trapping effect is more sensitive against the electrons than the holes at the low dopant concentration. This intrinsic characteristic causes the electron to be injected into the emitting layer first and then trapped in the bulk, producing a strong effect on device performance.