Hole injection polymer effect on degradation of organic light-emitting diodes

• We studied the degradation of OLED by capacitance–voltage measurements.
• We found charge accumulation at the HIL/HTL interface during operation.
• Charge accumulation leads to increase in operating voltage and decrease in luminance.
• Efficient HIL can suppress charge accumulation resulting in a more stable device.

Polythienothiophene:poly(perfluoroethylene-perfluoroethersulfonic acid) (PTT:PFFSA) has been used to enhance hole injection into small molecule OLEDs. Compared to devices with polyethylene dioxythiophene polystyrene sulfonate (PEDOT:PSS) as the hole injection layer (HIL), the OLED using PTT:PFFSA as a HIL gives enhanced efficiency and a slower luminance decay as well as a slower rise in operating voltage. Further studies of capacitance–voltage characteristics reveal that positive trapped charges accumulate in the hole transporting layer during operation. These results thus highlight the significance of hole injection layer to OLED operational stability.

Field distribution of a degraded HIL/NPB/Alq device under (a) a strong reverse bias and (b) a moderate forward bias before the electron injection occurs.Figure optionsDownload as PowerPoint slide