Methanol treatment on low-conductive PEDOT:PSS to PLED's performance

In order to achieve high device efficiency in blue-emitting polymer light-emitting diodes (PLED) and white-emitting PLED, low-conductive PEDOT:PSS Cievios (TM) P CH 8000 (8000) has been used to replace widely adopted high-conductive PEDOT:PSS Cievios (TM) P Al 4083 (4083). In a blue PLED with poly (dibenzothiophene-S,S-dioxide-co-9,9-dioctyl-2,7-fluorene) (PF-FSO) as the emission layer, though the 8000 device has a higher efficiency and a lower turn-on voltage than the 4083 device, the 8000 device exhibits low peak luminance, sharp efficiency roll-off, and permanent degradation of the emission material. By analyzing the hole-only device and the X-ray photoelectron spectroscopy spectra, it's revealed that the insulating PSS layer on 8000 surface is responsible for the inefficient hole injection. A simple methanol treatment on the 8000 surface effectively removes the redundant PSS. Without the insulating PSS layer, the hole injection becomes efficient which extends the recombination zone. As the result, the methanol-treated 8000 device not only retains low turn-on voltage and the high device efficiency of the untreated 8000 device, but also achieves the peak luminance, mild efficiency roll-off, and device stability of the 4083 device. (C) 2015 Elsevier B.V. All rights reserved.